panvk_meta_get_unorm_format_for_blk_size() requires a block size of 4
or less, but we didn't actually check for that before calling it. Fix
that, and also rename the function because what we actually care about
isn't whether it is a unorm format, but a blendable format.
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35771>
09b5802f9f