clocksource: Add a Kconfig menu

Move the clocksource Kconfig entries into their own menu, so that they
don't pollute the main device driver menu.
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: http://lkml.kernel.org/r/20140616114845.343e9960@endymion.delvareSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/clocksource/Kconfig

+menu "Clock Source drivers"
+
 config CLKSRC_OF
 	bool
 
@@ -207,3 +209,5 @@ config CLKSRC_VERSATILE
 	  counter available in the "System Registers" block of
 	  ARM Versatile, RealView and Versatile Express reference
 	  platforms.
+
+endmenu