Convert CONFIG_FSL_USDHC to Kconfig

This converts the following to Kconfig:
   CONFIG_FSL_USDHC

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Add IMX8M, TARGET_S32V234EVB to FSL_USDHC list]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index c6812f6..0ccb1ea 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -694,6 +694,13 @@
 	  This selects support for the i.MX eSDHC (Enhanced Secure Digital Host
 	  Controller) found on numerous Freescale/NXP SoCs.
 
+config FSL_USDHC
+	bool "Freescale/NXP i.MX uSDHC controller support"
+	depends on MX6 || MX7 ||ARCH_MX7ULP || IMX8 || IMX8M || TARGET_S32V234EVB
+	select FSL_ESDHC_IMX
+	help
+	  This enables the Ultra Secured Digital Host Controller enhancements
+
 endmenu
 
 config SYS_FSL_ERRATUM_ESDHC111