ARM/fbdev: sa11x0: Switch to use GPIO descriptors

This converts the SA11x0 frame buffer driver to use
GPIO descriptors. Get the GPIO optional and register
a look-up table specifically for the Shannon machine.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200415165055.193113-1-linus.walleij@linaro.org