msm: mdss: set the mdp core clock rate on 8x10

During the kernel initialization, we need to set
rate on the mdp core clock rate.  Otherwise, the
core clock rate is at its minimum, causing display
under-run on large panels.

Change-Id: Idcd69a758cbf3022f8ad6590b021f21dad5972b1
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>