More audio use case enhacements

- Use TW's "Call Main Mic" for "Speaker DMIC Endfire".
  - Resolves speakerphone echo by using only the main (bottom) mic.

- Clone "Handset" to "Line", as audio-caf uses "Line" by default now.
  - Also matches TW's "Main Mic".
d2: Disable entropy gathering for MMC device

 * Flash devices aren't a good source of entropy and contributing to the
   pool can be an expensive operation requiring needless locking.

Change-Id: I6073b38476706c2e678ecf980ca0a1546cda9125