Improved baudrate calculation function.

Uses 100% integer math, delivers more accurate results with fewer iterations in less time.

Since it seems most of the NXP chips use identical math, I have also altered the other targets in this commit.

If there are non-NXP chips which use a similar serial block, consider porting to those as well

Comparison:

         BAUD   DL MUL DIV  CPU_CLOCK
      -------  --- --- --- ----------
new: {   9600, 625,  1,  0,  96000000},	// Actual baud:    9600, error =0.00%,    1 iterations
old: {   9600, 625,  1,  0,  96000000},	// Actual baud:    9600, error =0.00%,    0 iterations

new: {  38400, 125,  4,  1,  96000000},	// Actual baud:   38400, error =0.00%,    8 iterations
old: {  38400,  81, 14, 13,  96000000},	// Actual baud:   38409, error +0.02%,  420 iterations

new: {  57600,  81,  7,  2,  96000000},	// Actual baud:   57613, error +0.02%,  120 iterations
old: {  57600,  54, 14, 13,  96000000},	// Actual baud:   57613, error +0.02%,  315 iterations

new: { 115200,  27, 14, 13,  96000000},	// Actual baud:  115226, error +0.02%,  120 iterations
old: { 115200,  27, 14, 13,  96000000},	// Actual baud:  115226, error +0.02%,  210 iterations

new: { 230400,  23, 15,  2,  96000000},	// Actual baud:  230179, error -0.10%,  120 iterations
old: { 230400,  17, 15,  8,  96000000},	// Actual baud:  230179, error -0.10%,  525 iterations

new: { 250000,  24,  1,  0,  96000000},	// Actual baud:  250000, error =0.00%,    1 iterations
old: { 250000,  24,  1,  0,  96000000},	// Actual baud:  250000, error =0.00%,    0 iterations

new: {1000000,   6,  1,  0,  96000000},	// Actual baud: 1000000, error =0.00%,    1 iterations
old: {1000000,   6,  1,  0,  96000000},	// Actual baud: 1000000, error =0.00%,    0 iterations

new: {2000000,   3,  1,  0,  96000000},	// Actual baud: 2000000, error =0.00%,    1 iterations
old: {2000000,   3,  1,  0,  96000000},	// Actual baud: 2000000, error =0.00%,    0 iterations

new: {   9600, 514, 15,  4, 100000000},	// Actual baud:    9600, error =0.00%,  110 iterations
old: {   9600, 337, 15, 14, 100000000},	// Actual baud:    9593, error -0.07%, 1365 iterations

new: {  38400,  93,  4,  3, 100000000},	// Actual baud:   38402, error +0.01%,  120 iterations
old: {  38400,  85, 12, 11, 100000000},	// Actual baud:   38363, error -0.10%,  525 iterations

new: {  57600,  62,  4,  3, 100000000},	// Actual baud:   57604, error +0.01%,  120 iterations
old: {  57600,  61,  9,  7, 100000000},	// Actual baud:   57633, error +0.06%,  840 iterations

new: { 115200,  31,  4,  3, 100000000},	// Actual baud:  115207, error +0.01%,  120 iterations
old: { 115200,  31,  4,  3, 100000000},	// Actual baud:  115207, error +0.01%,  525 iterations

new: { 230400,  19,  7,  3, 100000000},	// Actual baud:  230263, error -0.06%,  120 iterations
old: { 230400,  19,  7,  3, 100000000},	// Actual baud:  230263, error -0.06%,  735 iterations

new: { 250000,  25,  1,  0, 100000000},	// Actual baud:  250000, error =0.00%,    1 iterations
old: { 250000,  25,  1,  0, 100000000},	// Actual baud:  250000, error =0.00%,    0 iterations

new: {1000000,   5,  4,  1, 100000000},	// Actual baud: 1000000, error =0.00%,    8 iterations
old: {1000000,   5,  4,  1, 100000000},	// Actual baud: 1000000, error =0.00%,  315 iterations

new: {2000000,   2,  9,  5, 100000000},	// Actual baud: 2008929, error +0.45%,  120 iterations
old: {2000000,   2,  9,  5, 100000000},	// Actual baud: 2008929, error +0.45%,  315 iterations

new: {   9600, 625,  4,  1, 120000000},	// Actual baud:    9600, error =0.00%,    8 iterations
old: {   9600, 404, 15, 14, 120000000},	// Actual baud:    9602, error +0.02%, 1575 iterations

new: {  38400, 179, 11,  1, 120000000},	// Actual baud:   38408, error +0.02%,  120 iterations
old: {  38400, 101, 15, 14, 120000000},	// Actual baud:   38409, error +0.02%,  525 iterations

new: {  57600,  93,  5,  2, 120000000},	// Actual baud:   57604, error +0.01%,  120 iterations
old: {  57600,  68, 12, 11, 120000000},	// Actual baud:   57545, error -0.10%,  420 iterations

new: { 115200,  47, 13,  5, 120000000},	// Actual baud:  115248, error +0.04%,  120 iterations
old: { 115200,  34, 12, 11, 120000000},	// Actual baud:  115090, error -0.10%,  315 iterations

new: { 230400,  19,  7,  5, 120000000},	// Actual baud:  230263, error -0.06%,  120 iterations
old: { 230400,  17, 12, 11, 120000000},	// Actual baud:  230179, error -0.10%,  210 iterations

new: { 250000,  30,  1,  0, 120000000},	// Actual baud:  250000, error =0.00%,    1 iterations
old: { 250000,  30,  1,  0, 120000000},	// Actual baud:  250000, error =0.00%,    0 iterations

new: {1000000,   5,  2,  1, 120000000},	// Actual baud: 1000000, error =0.00%,    3 iterations
old: {1000000,   4,  8,  7, 120000000},	// Actual baud: 1000000, error =0.00%,  210 iterations

new: {2000000,   3,  4,  1, 120000000},	// Actual baud: 2000000, error =0.00%,    8 iterations
old: {2000000,   2,  8,  7, 120000000},	// Actual baud: 2000000, error =0.00%,  210 iterations
Merge pull request #116 from triffid/feature/NXP_improved-baudrate-calculation

NXP targets: Improved baudrate calculation function