serial: mpc512x: Properly define CONFIG_SYS_PSC3 in config files

Some of the boards using the mpc512x serial driver didn't properly
define which PSC console to use. This caused breakage when building
with CONFIG_SERIAL_MULTI enabled. Fix this by defining the default
PSC console.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Tom Rini <trini@ti.com>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Stefan Roese <sr@denx.de>
diff --git a/include/configs/aria.h b/include/configs/aria.h
index b21b495..0b31c50 100644
--- a/include/configs/aria.h
+++ b/include/configs/aria.h
@@ -322,6 +322,7 @@
  * Serial console configuration
  */
 #define CONFIG_PSC_CONSOLE		3	/* console on PSC3 */
+#define CONFIG_SYS_PSC3
 #if CONFIG_PSC_CONSOLE != 3
 #error CONFIG_PSC_CONSOLE must be 3
 #endif