ASoC: msm: fix the call drop during the device switch in voice call

During the powerup and powerdown of the HPHL and HPHR widget no
register is expected to be modified. So, the current implementation
uses virtual registers but since actual register values
are not modified, it results in inconsistent state during the
powerdown callback.
Replace the virtual register implementation with the virtual mux
widget present in the framework, which doesn't check against
change in register values during powerdown.

CRs-Fixed: 654640
Change-Id: I8c2ef0d601ecd8e8e659cf9d25e647631e9d4fd8
Signed-off-by: Aviral Gupta <aviralg@codeaurora.org>