add two new members to structs audio_encoding and audio_prinfo.

add two new members to structs audio_encoding and audio_prinfo.
for both structs, the new members are 'bps' and 'msb', which
describe the number of bytes per sample and data alignment in the
sample, respectively.  drivers must properly set these fields in
the 'query_encoding', 'set_parameters' and 'get_default_params'
hardware interface methods.

discussed with ratchov, deraadt