VKMS: New plane formats

[Simon Ser]

Ideally the final composition format would have enough precision for
all of the planes. I think it'd make sense to use ARGB16161616 if the
primary plane uses ARGB8888 and an overlay plane uses ARGB16161616.

To simplify the code, maybe it's fine to always use ARGB16161616 for
the output, and add getters which fetch an ARGB16161616 row for each
supported plane format.