arm: timer and interrupt init rework

actually the timer init use the interrupt_init as init callback
which make the interrupt and timer implementation difficult to follow

so now rename it as int timer_init(void) and use interrupt_init for interrupt

btw also remane the corresponding file to the functionnality implemented

as ixp arch implement two timer - one based on interrupt - so all the timer
related code is moved to timer.c

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/cpu/arm1176/s3c64xx/Makefile b/cpu/arm1176/s3c64xx/Makefile
index fa4ee3f..4656d9a 100644
--- a/cpu/arm1176/s3c64xx/Makefile
+++ b/cpu/arm1176/s3c64xx/Makefile
@@ -28,8 +28,8 @@
 
 LIB	= $(obj)lib$(SOC).a
 
-COBJS-y	= interrupts.o
 COBJS-$(CONFIG_S3C6400)	+= cpu_init.o speed.o
+COBJS-y	+= timer.o
 
 OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS-y))