[MIPS] add DECstation I/O ASIC clocksource

Add DECstation I/O ASIC clocksource

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/include/asm-mips/dec/ioasic.h b/include/asm-mips/dec/ioasic.h
index 486a5b0..98badd6 100644
--- a/include/asm-mips/dec/ioasic.h
+++ b/include/asm-mips/dec/ioasic.h
@@ -33,4 +33,6 @@
 
 extern void init_ioasic_irqs(int base);
 
+extern void dec_ioasic_clocksource_init(void);
+
 #endif /* __ASM_DEC_IOASIC_H */