Convert CONFIG_FSL_ESDHC_PIN_MUX to Kconfig

This converts the following to Kconfig:
   CONFIG_FSL_ESDHC_PIN_MUX

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index 5a5a31c..878f867 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -891,6 +891,10 @@
 	help
 	  This enables the Ultra Secured Digital Host Controller enhancements
 
+config FSL_ESDHC_PIN_MUX
+	bool "Perform esdhc device-tree fixup"
+	depends on (FSL_ESDHC || FSL_ESDHC_IMX) && OF_LIBFDT
+
 endmenu
 
 config SYS_FSL_ERRATUM_ESDHC111