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/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 17d0e73..14df2e9 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -609,7 +609,8 @@
 
 config MXC_UART
 	bool "IMX serial port support"
-	depends on MX5 || MX6 || MX7 || IMX8M
+	depends on ARCH_MX25 || ARCH_MX31 || TARGET_APF27 || TARGET_FLEA3 || TARGET_MX35PDK \
+		|| MX5 || MX6 || MX7 || IMX8M
 	help
 	  If you have a machine based on a Motorola IMX CPU you
 	  can enable its onboard serial port by enabling this option.