msm_fb : display : Block RGB downscale in MDP 4.0 and 4.1

Downscale is not allowed on RGB pipes in MDP 4.0 and 4.1. Hence,
fail the OVERLAY_SET ioctl for such configurations.

Change-Id: Ia18de77e78b84ec5f10a03fe9b48ef0821222e84
Signed-off-by: Pradeep Jilagam <pjilagam@codeaurora.org>
drivers: cleanup msm_dss_io_8x60