tdm_hwc: add fence api and backend interface

add fence api in tdm.h

tdm_error tdm_hwc_set_client_target_acquire_fence(tdm_hwc *hwc, int acquire_fence)
tdm_error tdm_hwc_get_commit_fence(tdm_hwc *hwc, int *commit_fence)
tdm_error tdm_hwc_window_set_acquire_fence(tdm_hwc_window *hwc_window, int acquire_fence)

tdm_common.h
TDM_HWC_CAPABILITY_FENCE

backend interface
tdm_error (*hwc_set_client_target_acquire_fence)(tdm_hwc *hwc, int acquire_fence)
tdm_error (*hwc_get_commit_fence)(tdm_hwc *hwc, int *commit_fence);
tdm_error (*hwc_window_set_acquire_fence)(tdm_hwc_window *hwc_window, int acquire_fence)

Change-Id: I706a27341fa14c6cd1bc4ec8fb49bd4f7a8079c8