msm8x10: Add mixer control to configure Rx/Tx channel

Provide mixer control command for number of rx/tx channels to be
configurable. Fixup function need to be splitted for rx/tx support.

Change-Id: I15cb6c55e8e3bf782ca31ca6dff6ae41eba99920
Signed-off-by: Fred Oh <fred@codeaurora.org>