formats: Unify handling of LA formats

With that we first try the ARB formats, and then, if the according entry
was not created, we try an emulation.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1174>
2 files changed