mdss: mdp: fix smmu power rail handoff configuration

mdss smmu driver turns on the power rail during probe
and leave it on for continuous splash screen scenario.
It avoids extra refcount during attach for this scenario
by relaying on MDP handoff status. However, MDP handoff
status is updated before context banks are attached for
video mode panel. This adds extra refcount to power rails
and leave them on always. This fix moves the power rail
handoff to smmu structure instead of relying on MDP
status.

Change-Id: Ifc98c0e3812c7b78224f0167886dcb49dba3b267
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>