Blackfin: fix GPTMR0_CLOCKSOURCE dependency on BFIN_GPTIMERS

The GPTMR0_CLOCKSOURCE Kconfig option requires the gptimers framework, so
make sure it is selected when this option is enabled.
Reported-by: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/Kconfig

@@ -648,6 +648,7 @@ config CYCLES_CLOCKSOURCE
 
 config GPTMR0_CLOCKSOURCE
 	bool "Use GPTimer0 as a clocksource (higher rating)"
+	select BFIN_GPTIMERS
 	depends on GENERIC_CLOCKEVENTS
 	depends on !TICKSOURCE_GPTMR0