disp: msm: dp: synchronize debug and aux common buffer handling

DP debug module is run by external script for automation testing.
DP aux and debug modules operate on shared buffers. In some race
conditions, aux and debug module can go out of sync resulting in
automation failures. Lock the buffers to make sure there are no
race conditions.

Change-Id: If0ae370c22cf035f3177666bd714221d6b3cd56e
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>