sbc: ARMv6 optimized version of analysis filter for SBC encoder

The optimized filter gets enabled when the code is compiled
with -mcpu=/-march options set to target the processors which
support ARMv6 instructions. This code is also disabled when
NEON is used (which is a lot better alternative). For additional
safety ARM EABI is required and thumb mode should not be used.

Benchmarks from ARM11:

== 8 subbands ==

$ time ./sbcenc -b53 -s8 -j test.au > /dev/null

real    0m 35.65s
user    0m 34.17s
sys     0m 1.28s

$ time ./sbcenc.armv6 -b53 -s8 -j test.au > /dev/null

real    0m 17.29s
user    0m 15.47s
sys     0m 0.67s

== 4 subbands ==

$ time ./sbcenc -b53 -s4 -j test.au > /dev/null

real    0m 25.28s
user    0m 23.76s
sys     0m 1.32s

$ time ./sbcenc.armv6 -b53 -s4 -j test.au > /dev/null

real    0m 18.64s
user    0m 15.78s
sys     0m 2.22s

0 files changed, 0 insertions, 0 deletions