disp: msm: check max FPS of DFPS to update UIDLE configurations

It is not applicable for all DFPS cases to update UIDLE state
according to current frame rate. If DFPS changes frame rate
through vertical front porch values, the SDE clocks and transfer
time will not get changed accordingly, and it always get fixed
at max frame rate configuration of DFPS.
Add this change to check max FPS of DFPS instead of current
frame rate for UIDLE update, if DFPS is enabled with VFP.

Change-Id: I7634bce6a9eb1af212ba19a267735be08b20ae1f
Signed-off-by: Lei Chen <chenlei@codeaurora.org>