mdss: msm: keep smmu power rail on during continuous splash

SMMU clocks and regulators should be on during continuous
splash screen scenario. Turning them off causes the underrun.
This change leaves these power rail on during probe and avoids
additional refcount during attach. This refcount will be removed
on detach during first suspend-resume.

Change-Id: I70570dea67d9a95e86ddbe892252dcb493c8fa65
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>