disp: msm: sde: skip unnecessary cache register programming

Plane update will call system cache update, and by default,
will clear any cache programming. This clear is only necessary
after returning from a cached state. This change will reduce
unnecessary programming and event logs if the sys cache
was previously disabled and remains disabled.

Change-Id: I7f560ff24990a8c7ad785e560873193b7bf3a491
Signed-off-by: Nilaan Gunabalachandran <ngunabal@codeaurora.org>