msm: mdss: Add low persistence mode support for display

Snapshot of low persistence mode changes as of
26cfe58bd94a ("msm: mdss: Add support for low persistence
display mode") and a805a3e1e791 ("arm64/dts: angler: Don't
blank screen when leaving low persistence mode"), to add
low persistence mode support for display. Also, add some
changes to optimize the implementation for LP mode and
fix crash issue when VR APP is up.

CRs-Fixed: 1104888 1108207
Change-Id: I509fb5c87d93e2416882942a226cb9b48bc1d3bf
Signed-off-by: Yahui Wang <yahuiw@codeaurora.org>