msm: mdss: avoid registers access during validate

During validate ioctl, there is no need to access
some of the registers this early on time.
This patch moves the register programming from
validate to commit, so mdp clocks do not need
to be enabled during validate, preventing
unnecessary toggling of the clocks once those
have been released in command mode panels.

Change-Id: I3eb34221d245153fad14463b873d0b870f5eb62a
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>