ASOC: msm: Cache sample rate and channels when backend active.

While handling device switch between headset and stereo speaker
during FM playback, the front end will be torn down
(after playing tone) while keeping the backend active for FM.
During this time, hardware param will no longer be active.
Platform driver was using this invalid hardware parameters to
configure the matrix in the dsp with sample rate and channel.
Sometimes invalid sample rate being sent to DSP was causing
a crash in DSP. To overcome the issue, platform driver needs to
cache sample rate and channel information when backend
is active while front end is being torn down and setup
again. This cached information will be used to configure
the adm when front end is setup again.

Change-Id: I7fb976b42a56602ad99f4262b6f4d0c986e2ad5a
CRs-fixed: 347115
Signed-off-by: Bharath Ramachandramurthy <bramacha@codeaurora.org>