st/mesa: expose EXT_vertex_array_bgra when supported by backend
st/mesa: expose EXT_vertex_array_bgra when supported by backend

Signed-off-by: Christian Gmeiner <7d98dcb0e8545320ffc03d45630c91ed21ec4c41@gmail.com>
Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler