sbc: Add encoder_state to analysis functions

Until now, SIMD analysis used to process 4 blocks of 8 samples at a
time. This was implemented using two constant tables: odd and even. This
mean we can only process 4, 8, 12, or 16 blocks par SBC packets.
mSBC requires 15 blocks, so to be able to analyse 1 block, it will be
necessary to know if we are processing an odd or even block. This will
be done with a new member to encoder_state.
sbc: Break 4 blocks processing to variable steps

Until now SBC processed 4 blocks at a time. If we want to process 15
blocks, then we need to break this processing in one block steps. 4
blocks is still default increment.
sbc: Rename sbc_analyze_4b_xx to sbc_analyze_xx
sbc: Add mmx primitive for 1b 8s analysis
sbc: Add armv6 primitive for 1b 8s analysis
sbc: Add iwmmxt primitive for 1b 8s encoding
sbc: Add plain C primitive for 1b 8s analysis
sbc: Use plain C primitive if doing msbc on neon

neon has it's own optimized input reordering. Until this code gets optimized,
the neon assembly code will not work with the mSBC input reordering.
However, the plain C version of mSBC can be used in this case.
This patch makes use of plain C code if the block increment is 1 which is
typical for mSBC.
sbc: Fix input reordering for 15 blocks case

SBC analysis handles 8 samples at a time. The optimisation requires 8
samples forming an "odd" block, followed by 8 samples, forming an "even"
block. Until now SBC was used for encoding 4, 8, 12, or 16 blocks in a
frame. Reordering took a frame and for each 16 samples (ie 2 blocks) it
produced one "odd" block and one "even" block.
A mSBC frame encodes 15 blocks of 8 samples. 14 blocks are processed as
before, two at a time. If 8 samples are remaining, it will form the
first half of two blocks (a bit of an "odd" block, and a bit of an
"even" block). When processing the next frame, we detect eight samples
were missing at previous iteration and the two block can be finished.

This reordering is possible because only one sample is moved (x[-7]) AND
the first coefficient in the coef table is 0. Thus x[0] doesn't need to
be set and 0 can be used in calculation instead. Note that x[-7] is not
used in analysis for this block.
see: analysis_consts_fixed8_simd_odd.

To detect that two blocks are not completed, the number of processed
samples can be used. This value is stored in position. position starts
at SBC_X_BUFFER_SIZE-72 and is decremented by 16 as long as two blocks
can be formed. If only 8 samples are remaining in input, then position
is decremented by 8 *arbitrarly*, thus indicating that some samples are
pending. During next frame reordering, position will be decremented by 8
again, back to a 16 multiple.

This logic works for SBC_X_BUFFER_SIZE-72 multiple of 16 and bigger than
8*2*15+72=312 and less than 8*3*15+72=432. The current value of 328
matches this constraint and X buffer is shifted every two frames (30
blocks) in mSBC. This way, we don't need to care about x[-7] when
shifting, we also know that it won't be before X.
sbc: Add a private boolean flag to enable 15 block encoding

This patch introduce a new private member which purpose is to encode 15
blocks. It is private to the library and can't be set from standard API.
sbc_init_msbc() function will be defined to set this flag.
sbc: Declare and implement sbc_init_msbc
sbc: Add support for mSBC frame header

Traditionnal SBC frame header describe encoding parameters for each
frame: nr of blocks, subbands, allocation method, and bitpool. In mSBC,
only one combination of parameter is defined. That combination cannot be
expressed using a traditionnal SBC header. Because of this, a specific
header is defined with 0xAD followed by two reserved zero bytes.
sbc: Update sbcdec for msbc
sbc: Update sbcenc for msbc
sbc: Update sbcinfo for msbc
TODO: Add TODO list
Add sample.au
Add test scripts
sbc: Arm and neon tests scripts