spi: mediatek: merge all identical compat to mtk_common_compat

This patch merge all identical compat into on mtk_common_compat
and used for all compatible soc.

Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>