Convert CONFIG_FSL_USDHC to Kconfig

This converts the following to Kconfig:
   CONFIG_FSL_USDHC

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/imx8mn_evk_defconfig b/configs/imx8mn_evk_defconfig
index 37ce46e..3ee15d3 100644
--- a/configs/imx8mn_evk_defconfig
+++ b/configs/imx8mn_evk_defconfig
@@ -65,7 +65,7 @@
 CONFIG_MMC_UHS_SUPPORT=y
 CONFIG_MMC_HS400_ES_SUPPORT=y
 CONFIG_MMC_HS400_SUPPORT=y
-CONFIG_FSL_ESDHC_IMX=y
+CONFIG_FSL_USDHC=y
 CONFIG_PHYLIB=y
 CONFIG_DM_ETH=y
 CONFIG_PINCTRL=y