ARM: cleanup duplicated exception handlingcode

Move duplicated exception handling code into lib_arm.

Signed-off-by: Andreas Engel <andreas.engel@ericsson.com>
diff --git a/cpu/arm_intcm/Makefile b/cpu/arm_intcm/Makefile
index d5ac7d3..7701b03 100644
--- a/cpu/arm_intcm/Makefile
+++ b/cpu/arm_intcm/Makefile
@@ -26,7 +26,7 @@
 LIB	= $(obj)lib$(CPU).a
 
 START	= start.o
-COBJS	= interrupts.o cpu.o
+COBJS	= cpu.o
 
 SRCS	:= $(START:.o=.S) $(SOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS) $(SOBJS))