glamor: add support for NV12 in Xv

Useful when video decoders only output NV12. Currently
glamor Xv only supports I420 and YV12.

Note that Intel's sna supports I420, YV12, YUY2, UYVY, NV12.

Test: xvinfo | grep NV12
Test: gst-launch-1.0 videotestsrc ! video/x-raw, format=NV12 ! xvimagesink

v2: Combine the two texture2Ds on u_sampler.

Signed-off-by: Julien Isorce <jisorce@oblong.com>
Tested-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
1 job for glamor-xv-nv12 in 3 minutes and 19 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Test
passed job #22985

00:03:19