Add HW volume control via ES9018K2M, and reorganize
eros_qn_codec.c/.h, audiohw-erosqnative.c.
This automatically detects the presence of the new DAC and
uses its hardware volume scaling. If not present, use same
SWVOL we have been using so far.
Add debug menu readout of SWVOL/I2C result.
Break out es9018k2m stuff into its own file so that
maybe it can be useful to other ports.
Note that we may need to get smarter about detecting the DAC
type if/when another model emerges.
Change-Id: I586a1cf7f150dd6b4e221157859825952840af56
