at91: add support for the PM9263 board of Ronetix GmbH

The PM9263 board is based on the AT91SAM9263-EK board.

Here is the page on Ronetix website:
http://www.ronetix.at/starter_kit_9263.html

Signed-off-by: Ilko Iliev <iliev@ronetix.at>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/cpu/arm926ejs/at91/lowlevel_init.S b/cpu/arm926ejs/at91/lowlevel_init.S
index ec6ad5d..54b3f3d 100644
--- a/cpu/arm926ejs/at91/lowlevel_init.S
+++ b/cpu/arm926ejs/at91/lowlevel_init.S
@@ -30,6 +30,8 @@
 #ifndef CONFIG_SKIP_LOWLEVEL_INIT
 
 .globl lowlevel_init
+.weak lowlevel_init
+.set lowlevel_init,function
 lowlevel_init:
 
 	/*