mmc: sunxi-mmc: Drop unused includes

The Sunxi MMC driver uses slot GPIO helpers and does not make
any use of <linux/gpio.h> or <linux/of_gpio.h> so drop these
surplus includes.

Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: cenowy Zheng <icenowy@aosc.io>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>