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