pixel-formats: Add NV15/20/30 YUV 10bpc formats

NV15/20/30 are a family of 10bpc YUV formats which have 4
horizontally-adjacent samples packed into a 40-bit cluster. The
difference between 15/20/30 is in the subsampling.

No fallbacks are provided, as there is no format pairing which would
allow us to sensibly unpack the clusters.

Signed-off-by: Daniel Stone <daniels@collabora.com>