Blackfin: add support for gptimer0 as a tick source

For systems where the core cycles are not a usable tick source (like SMP
or cycles gets updated), enable gptimer0 as an alternative.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/arch/blackfin/include/asm/time.h b/arch/blackfin/include/asm/time.h
index ddc43ce..589e937 100644
--- a/arch/blackfin/include/asm/time.h
+++ b/arch/blackfin/include/asm/time.h
@@ -37,4 +37,5 @@
 extern unsigned int __bfin_cycles_mod;
 #endif
 
+extern void __init setup_core_timer(void);
 #endif