hwcomposer: Add sourceTransform to hwc_layer_t

sourceTransform has the source buffer transform which can used to
apply rotation on displays whose orientation is fixed(HDMI).

CRs-fixed: 387357
Change-Id: I26eb2de76b3548634a80ca8b98547c6fdfe145ea
(cherry picked from commit f16aed381eb2a7232bf576c1d77cdad61be54419)