arm920t/interrupts: Move conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/cpu/arm920t/interrupts.c b/cpu/arm920t/interrupts.c
index ea24cdf..539eb5c 100644
--- a/cpu/arm920t/interrupts.c
+++ b/cpu/arm920t/interrupts.c
@@ -30,9 +30,8 @@
  */
 
 #include <common.h>
-
-#ifdef CONFIG_USE_IRQ
 #include <asm/proc-armv/ptrace.h>
+
 void do_irq (struct pt_regs *pt_regs)
 {
 #if defined (ARM920_IRQ_CALLBACK)
@@ -46,4 +45,3 @@
 #error do_irq() not defined for this cpu type
 #endif
 }
-#endif