drm/msm: add ability to flag properties as dirty

This patch adds a new msm_property function to allow clients
to explicitly flag a property as being dirty. This is helpful
if certain properties need to be conditionally reevaluated
even if their values haven't changed.

CRs-Fixed: 2062083
Change-Id: Ic510c618587508f8602bfb03ad57a1047309e4f2
Signed-off-by: Clarence Ip <cip@codeaurora.org>