Use actual kernel headers and display-caf paths if defined

Change-Id: I7338867f6eb4d88b33b610a2b2f93280ed6e71bc

Conflicts:
	libc2dcolorconvert/Android.mk

	modified:   libc2dcolorconvert/Android.mk
	modified:   mm-video-legacy/DivxDrmDecrypt/Android.mk
	modified:   mm-video-legacy/vidc/vdec/Android.mk
	modified:   mm-video-legacy/vidc/vdec/inc/omx_vdec.h
	modified:   mm-video-legacy/vidc/vdec/src/omx_vdec.cpp
	modified:   mm-video-legacy/vidc/venc/Android.mk
	modified:   mm-video-v4l2/vidc/vdec/Android.mk
	modified:   mm-video-v4l2/vidc/venc/Android.mk