msm: mdss: fix transitions from off to doze mode

When doze mode is requested while the panel in powered off, the
panel needs to be first unblanked and then configured into low power
mode. While this sequence exists in the current implementation,
the execution sequence only calls MDP's on function while unblanking
the panel. The correct approach is to go through the full unblank
sequence which would also start the display commit thread. Without
this, screen updates while in doze mode will not work and could
lead to unexpected behaviors.

Change-Id: I4f65764acaf01d61d129e00179930af9ebb79c77
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>