Use vaapi to do rgb->yuv420p color conversion

Enable window capture for amd/intel.
Properly check if h264/hevc is supported on amd/intel before using
codec.

project.conf

@@ -13,4 +13,5 @@ xcomposite = ">=0.2"
 xrandr = ">=1"
 libpulse = ">=13"
 libswresample = ">=3"
-libavfilter = ">=5"
+libavfilter = ">=5"
+libva = ">=1"