drm/msm: add 2700 ns delta for sde rsc mode threshold

Current configuration updates mode threshold and backoff
time to same value and it can cause rsc qtimer value
setting to less than "current time". Avoid this race
condition for corner cases by adding 2700 ns time delta
in mode threshold programming.

Change-Id: I034b3b1d22ab5fdfda2cee4c251165da5e0aa0f6
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>