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/mach-bf561/Kconfig b/arch/blackfin/mach-bf561/Kconfig
index 6965dd5..cb97436 100644
--- a/arch/blackfin/mach-bf561/Kconfig
+++ b/arch/blackfin/mach-bf561/Kconfig
@@ -125,6 +125,7 @@
 	default 9
 config IRQ_TIMER0
 	int "TIMER 0  Interrupt"
+	default 7 if TICKSOURCE_GPTMR0
 	default 8
 config IRQ_TIMER1
 	int "TIMER 1  Interrupt"