Add header for dsscomp and optional bltsville data from Android HWC

In order to support the OMAP4470 GC320 blit IP from HWC, we will
optionally add blit data to the payload of information passed from
HWC to the SGX display driver (OMAPLFB).

Change-Id: Ia764810b0db0d5d7b0e3f777eeabf879b4552282
Signed-off-by: Tony Lofthouse <a0741364@ti.com>
omap_hwc: Describe the api agreement with omaplfb

Change-Id: I1ec9348a661999d536dcec1ba47247289075790e
Signed-off-by: Tony Lofthouse <a0741364@ti.com>