mmc: sdhci-imx-esdhc: adopt pinctrl support

Cc: linux-mmc@vger.kernel.org
Cc: Chris Ball <cjb@laptop.org>
Signed-off-by: Dong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>