serial: pxa: Make use of default_serial_console in serial_pxa

Make use of the newly implemented weak default_serial_console in
the serial_pxa driver. This removes all reimplementations of this
function from board files.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Tom Rini <trini@ti.com>
diff --git a/include/configs/xaeniax.h b/include/configs/xaeniax.h
index e399e95..eee2547 100644
--- a/include/configs/xaeniax.h
+++ b/include/configs/xaeniax.h
@@ -54,7 +54,7 @@
  */
 #define CONFIG_PXA_SERIAL
 #define CONFIG_BTUART	       1       /* we use BTUART on XAENIAX */
-
+#define CONFIG_CONS_INDEX	4
 
 /* allow to overwrite serial and ethaddr */
 #define CONFIG_ENV_OVERWRITE