gallium: Add util_format_is_unorm8 check
Useful for formats that would work with the same driver code path as RGBA8 UNORM but that don't meet the util_format_is_rgba8_variant criteria due to a smaller channel count.
Signed-off-by: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com
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See panfrost render target series for use.