Convert CONFIG_MXC_UART to Kconfig

This converts the following to Kconfig:
   CONFIG_MXC_UART

Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
diff --git a/configs/mx6memcal_defconfig b/configs/mx6memcal_defconfig
index 01a0fff..15e10ea 100644
--- a/configs/mx6memcal_defconfig
+++ b/configs/mx6memcal_defconfig
@@ -42,6 +42,7 @@
 CONFIG_DM=y
 # CONFIG_MMC is not set
 CONFIG_FSL_USDHC=y
+CONFIG_MXC_UART=y
 CONFIG_USB=y
 CONFIG_USB_GADGET=y
 CONFIG_USB_GADGET_MANUFACTURER="FSL"