We have handled the GFX register case for quite some time now.

Cc: Johnny Huang <johnny_huang@aspeedtech.com>
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Acked-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20190628023838.15426-6-andrew@aj.id.auSigned-off-by: Linus Walleij <linus.walleij@linaro.org>