SurfaceFlinger: update sourceTransform in hwc_layer_t

set the sourceTransform in hwc_layer_t to the bufferOrientation,
which will be used for setting the orientation on external display

CRs-fixed: 387357
Change-Id: I7ae6a818001eb41a9209dea166dc9232de182fe5
(cherry picked from commit 608db1fa7aa4dee3fc0359bd5686a74e2dfc9d40)

Conflicts:
	services/surfaceflinger/Layer.cpp