drm: gma500: Convert to GPIO descriptors

Finalize he conversion of GMA500 to use only GPIO descriptors.
The GPIO look-up-table is associated with the device directly
in the GMA500 Medfield chip driver since no explicit platform
type device (such as in x86/platform/intel-mid) exists: the
GMA500 probes directly from the PCI device. Apparently GPIOs
128 and 34 are used on all of these so just go ahead and
register those for resetting the DSI pipes.

Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200703125901.513476-1-linus.walleij@linaro.org