neon fast quantizer updated

vp8_fast_quantize_b_neon function updated and further optimized.
 - match current C implementation of fast quantizer
 - updated to use asm_enc_offsets for structure members
 - updated ads2gas scripts to handle alignment issues

Change-Id: I5cbad9c460ad8ddb35d2970a8684cc620711c56d
8 files changed