driver/mxc_i2c: Move static data structure to global_data

This driver needs a data structure in SRAM before SDRAM is available.
This is not alway the case using .data section. Moving this data
structure to global_data guarantees it is writable.

Signed-off-by: York Sun <yorksun@freescale.com>
CC: Troy Kisky <troy.kisky@boundarydevices.com>
drivers/i2c/fsl_i2c: modify i2c_read to handle multi-byte write

Most of the I2C slaves support accesses in the typical style
that is : read/write series of bytes at particular address offset.
These transactions look like:"
(1) START:Address:Tx:Offset:RESTART:Address[0..4]:Tx/Rx:data[0..n]:STOP"

However there are certain devices which support accesses in
terms of the transactions as follows:
(2) "START:Address:Tx:Txdata[0..n1]:Clock_stretching:
        RESTART:Address:Rx:data[0..n2]"
Here Txdata is typically a command and some associated data,
similarly Rxdata could be command status plus some data received
as a response to the command sent.

Type (1) transactions are currently supportd in the
i2c driver using i2c_read and i2c_write APIs. I2C EEPROMs,
RTC, etc fall in this category.

To handle type (2) along with type (1) transactions,
i2c_read() function has been modified.

Signed-off-by: Shaveta Leekha <shaveta@freescale.com>
Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>