Fix QP setting for CBR mode
Fix QP setting for CBR mode

The QP specified in MFX_AVC_SLICE_STATE is also used as the starting
QP in the first MB of a slice. In addition, add assertions for QP releated
setting for 8-bit pixel bit-depth support

Signed-off-by: Xiang, Haihao <8d677183e5993577d4fa73a419b76987913292d6@intel.com>
Signed-off-by: Rogozhkin, Dmitry V <01f0df9cc32cbf6a7f0faa5c8376e6cf28354d70@intel.com>

gbeauchesne/libva-intel-driver,uartie/vaapi-intel-driver,gbeauchesne/libva-intel-driver,halleyzhao/libva-intel-driver-fdo,01org/iotg-lin-gfx-va-driver,01org/iotg-lin-gfx-va-driver,halleyzhao/libva-intel-driver-fdo,chenxianqin/vaapi-intel-driver,gbeauchesne/libva-intel-driver,uartie/vaapi-intel-driver,gbeauchesne/libva-intel-driver,uartie/vaapi-intel-driver,halleyzhao/libva-intel-driver-fdo,01org/iotg-lin-gfx-va-driver,halleyzhao/libva-intel-driver-fdo,uartie/vaapi-intel-driver,uartie/vaapi-intel-driver,chenxianqin/vaapi-intel-driver,gbeauchesne/libva-intel-driver,01org/iotg-lin-gfx-va-driver,chenxianqin/vaapi-intel-driver,chenxianqin/vaapi-intel-driver,chenxianqin/vaapi-intel-driver,01org/iotg-lin-gfx-va-driver