Incorrect video output configuration bits were being tested on pins in
GPIO banks AA and AB for the ROM{8,16} mux functions. The ROM{8,16}
functions are the highest priority for the relevant pins and also the
default function, so we require the relevant video output configuration
be disabled to mux GPIO functionality. As the wrong bits were being
tested a GPIO export would succeed but leave the pin in an unresponsive
state (i.e. value updates were ignored).

This misbehaviour was discovered as part of extending the GPIO
controller's support to cover banks Y, Z, AA, AB and AC (AC in the case
of the g5 SoC).

Fixes: 6d329f14 ("pinctrl: aspeed-g4: Add mux configuration for all pins")
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>