overlay: Add support for rotator downscale

Add support for rotator downscale. This is enabled from 8994 onwards
Constraints:
--Downscale should be a power of 2, max upto 32
--Both directions should have equal downscale
--{src_w, src_h} mod downscale = 0
--No BWC
--No Interlaced video support

The rotator's destination rect is modified to reflect the presence of
downscale. Any downscale calcs should be done only after adjusting
crop to meet rotator's requirements.

Smaller downscale is used if we need to chop off any more than 1
line or pixel.

Change-Id: Id07d62fefa3213035f16cca49497800716484a95