st/va: enable vbr rate control for vaapi encode

This patch enables variable bit-rate for vaapi encoding. According to va.h,
target bit-rate equals to maximum bit-rate multiplies by target_percentage.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
2 files changed