drm/msm/sde:remove horz and vert decimation support for Kona

This change adds the ability to disable decimation when
it is not supported. Setting decimation to true will default
it to the current maximum decimation supported by the targets.
If decimation property is not set, max horizontal and vertical
decimation will be set to 0.

Change-Id: Id26b32bba0707a7c24a1954568ad098d982674ce
Signed-off-by: Samantha Tran <samtran@codeaurora.org>