disp: include: add pre-downscale fields to scaler config

Add fields required by kernel for setting up the pre-downscale
HW block during an inline rotation session. This increases
the inline rotation maximum downscale ratio for targets which
have the pre-downscale hardware.

Change-Id: I7aa43af2ede740fb0fe3ab6c9a715d1aebad6417
Signed-off-by: Steve Cohen <cohens@codeaurora.org>