serial_mx31: allow it to work with mx27 too and rename to serial_mxc

UART hardware on i.MX27 is the same as on the i.MX31 so we just
need to provide the driver with correct address of the registers.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
diff --git a/include/configs/imx31_phycore.h b/include/configs/imx31_phycore.h
index cbc0b92..cb42a7c 100644
--- a/include/configs/imx31_phycore.h
+++ b/include/configs/imx31_phycore.h
@@ -64,7 +64,7 @@
 #define CONFIG_SYS_I2C_SPEED		100000
 #define CONFIG_SYS_I2C_SLAVE		0xfe
 
-#define CONFIG_MX31_UART	1
+#define CONFIG_MXC_UART	1
 #define CONFIG_SYS_MX31_UART1		1
 
 /* allow to overwrite serial and ethaddr */