mmc: host: sdhci-s3c: Use devm_gpio_request to request GPIOs

The set of GPIO pins used by sdhci-s3c driver varies between
configurations, such as card detect method, pinctrl availability, etc.
This overly complicates the code requesting and freeing GPIO pins, which
must check which pins are used, when freeing them.

This patch modifies the sdhci-s3c driver to use devm_gpio_request to
free requested pins automatically after unbinding the driver.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>