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/lib_arm/board.c b/lib_arm/board.c
index e3040ac..c7768e5 100644
--- a/lib_arm/board.c
+++ b/lib_arm/board.c
@@ -266,7 +266,10 @@
 	arch_cpu_init,		/* basic arch cpu dependent setup */
 #endif
 	board_init,		/* basic board dependent setup */
+#if defined(CONFIG_USE_IRQ)
 	interrupt_init,		/* set up exceptions */
+#endif
+	timer_init,		/* initialize timer */
 	env_init,		/* initialize environment */
 	init_baudrate,		/* initialze baudrate settings */
 	serial_init,		/* serial communications setup */