msm: bam_dmux: increase shutdown logging granularity

In the power collapse shutdown path, some of the major events are grouped
together in the span between two log statements.  It is difficult to tell
which event might be the cause or victim of a delay.

Add a few additional log statements to help identify when exactly each
major event occurs to assist debugging any possible delays.

Change-Id: I904f1be98b57026bd2499b034c8113c01afb1869
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>