disp: msm: sde: avoid cpu wakeup with vsync event timer

Vsync event timer wakeup was designed to reduced the
interrupt latency and trigger retire fence without delay.
This is fixed by avoiding CPU power collapse where MDSS
interrupt is scheduled. This change avoids extra CPU
wakeup.

Change-Id: Iadaf0e2b84fb079bbc64d9201230df54f8dbe8c1
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>