drm/msm/sde: add support for PA VLUT version 1.8

VLUT in PA block is used by ABA features to adjust the
contrast. Change adds support for PA VLUT 1.8 AHB path
to enable/disable VLUT control, set VLUT data, and enable
VLUT flush bit.

Change-Id: I80167f866d051f43341f6272312bfc74195dd46d
Signed-off-by: Xu Yang <yangxu@codeaurora.org>