mdss: mdp: Add downscale factor for rotator

Newer chipsets supports rotator downscale upto 1/64.
Add rotator downscale min and max value in MDP caps, so that
SDM can read the value from mdp caps and perform downscale.
SDM assumes rotator downscale max as 64, if driver does not
populate via mdp caps.

Change-Id: I9cc2ffc8a11e9da208e9b7bc67c09b3f57bc7a63
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>