msm: sde: Correct max downscale factor for SDE rotator

Max downscale factor for UBWC format is 4.0, and max downscale factor
for TP10/TP10_UBWC format is 2.0, and should be based on source format.
Also we need to add downscale factor capability reporting to allow
usermode driver to select correct scaling setting.

CRs-Fixed: 1086805
Change-Id: Id92eabf03c8dace1c0ff801504b8591e9121782d
Signed-off-by: Benjamin Chan <bkchan@codeaurora.org>