drm/msm/sde: add mutex lock for crtc color processing list

Race condition happenes when multithread accessing the crtc
list. The change adds mutex lock for the lists to avoid race
condition issue.

Print out event type when error happenes in dmesg.

CRs-fixed: 2108048
Change-Id: I0103567eba1498b425ff799f56c43fb9f23b4c5a
Signed-off-by: Xu Yang <yangxu@codeaurora.org>