video: fbdev: omapfb: lcd_ams_delta: use GPIO lookup table

Now as Amstrad Delta board - the only user of this driver - provides
GPIO lookup tables, switch from GPIO numbers to GPIO descriptors and
use the table to locate required GPIO pins.

Declare static variables for storing GPIO descriptors and replace
gpio_ function calls with their gpiod_ equivalents. Move GPIO lookup
to the driver probe function so device initialization can be deferred
instead of aborted if a GPIO pin is not yet available.

Pin naming used by the driver should be followed while respective GPIO
lookup table is initialized by a board init code.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Boris Brezillon <boris.brezillon@bootlin.com>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>