Add one flag to use the qp_delta instead of qp priority for ROI under non-CQP mode

Add one flag to use the qp_delta instead of qp priority for ROI under non-CQP mode

Currently the roi_value in VAEncROI is used as the qp priority when
VAConfigAttribRateControl != VA_RC_CQP. But some customers hope to use
it as qp_delta like CQP mode. In such case one flag is added to indicate
whether it is qp_priority or not. At the same time driver can export it
in VAConfigAttribValEncROI to indicate whether the qp_delta is supported
when VAConfigAttribRateControl != VA_RC_CQP.

v2: update comments in va.h

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: ceciliapeng <cecilia.peng@intel.com>
Signed-off-by: Pengfei Qu <Pengfei.Qu@intel.com>
Signed-off-by: Xiang, Haihao <haihao.xiang@intel.com>
Reviewed-by: Sean V Kelley <seanvk@posteo.de>