va: encoder: Add QVBR and ICQ rate control support
These two modes are similar to CRF mode in x264, which is its default rate control mode. More and more users want us to support this, and FFMpeg VAAPI encoder already supports that.
These two modes are similar to CRF mode in x264, which is its default rate control mode. More and more users want us to support this, and FFMpeg VAAPI encoder already supports that.