drm/msm/sde: Add support for mdp LUT memory retention for display

When crtc is enabled, set mdp lut memory retention flag to retain
memory for color processing features; when crtc is disabled, set
mdp lut memory retention flag to not retain the memory.

Change-Id: I6d4c09b4ed05cb6bd85248c40dda214ad670dac2
Signed-off-by: Ping Li <pingli@codeaurora.org>