hwc: Ensure borderfill pipe is setup only after unblank

MDP operations should not be done in blank mode. Ensure that the
borderfill pipe is configured in prepare which happens after
unblank.

Change-Id: I97e75ab732015e0f02d12a24af37e4ed86b6b090

Conflicts:
	libhwcomposer/hwc_utils.cpp
	libhwcomposer/hwc_utils.h
Merge "hwc: Ensure borderfill pipe is setup only after unblank"