arm: unify interrupt init

all arm init the IRQ stack the same way
so unify it in lib_arm/interrupts.c and then call arch specific interrupt init

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/cpu/arm720t/interrupts.c b/cpu/arm720t/interrupts.c
index ff21314..91d552c 100644
--- a/cpu/arm720t/interrupts.c
+++ b/cpu/arm720t/interrupts.c
@@ -111,7 +111,7 @@
 static ulong lastdec;
 
 #if defined(CONFIG_USE_IRQ) && defined(CONFIG_S3C4510B)
-int interrupt_init (void)
+int arch_interrupt_init (void)
 {
 	int i;