MIPS: stub interrupt_init function

interrupt_init is called unconditionally by the generic board code.
Define a stub for it on MIPS like the enable & disable functions.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>

arch/mips/cpu/mips32/interrupts.c

@@ -7,6 +7,11 @@
 
 #include <common.h>
 
+int interrupt_init(void)
+{
+	return 0;
+}
+
 void enable_interrupts(void)
 {
 }

arch/mips/cpu/mips64/interrupts.c

@@ -7,6 +7,11 @@
 
 #include <common.h>
 
+int interrupt_init(void)
+{
+	return 0;
+}
+
 void enable_interrupts(void)
 {
 }