msm: mdss: Add core clock level selection in MDSS

Currently core clock is calculated for each frame and
depending upon the calculated value clock driver rounds it
to the nearest clock level from clock table. Now do
quantization of required clock rate at mdp driver itself
once before the request goes to clock driver.

Change-Id: Ie30947fb8f7d2978bb121b28920c05888332bf3f
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>