mmc: sdhci-bcm-kona: Drop unused includes

The SDHCI BCM Kona 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: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>