mmc: host: sdhci-s3c: Add support for pinctrl

This patch adds support for pin configuration using pinctrl subsystem
to the sdhci-s3c 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>