drm/vc4: hdmi: Convert to gpiod

The new gpiod interface takes care of parsing the GPIO flags and to
return the logical value when accessing an active-low GPIO, so switching
to it simplifies a lot the driver.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210524131852.263883-2-maxime@cerno.tech