msm: mdss: use usleep_range instead of msleep in mdss util

msleep API runs in atomic context and can add extra delay
after sleep timeout. This can add extra delays for panel
regulator turn on/off sequence which affects device
suspend/resume timing. Moving to usleep_range enables the
delay backed by hrtimers.

Change-Id: Id9e50ab02c0166de41316eeb948e93cdce432e15
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>