msm: mdss: Program linear GC LUT as default for rounding

Programming layer mixer GC linear LUT as default. This
would configure the GC of layer mixer out of bypass and
enable better rounding of pixel values in hardware.

Change-Id: I3c9a5687101972dad48402ab7717e5e940c85215
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>