x86_64: Select clocksource watchdog in Kconfig

TSC must be verified by a continous and reliable clocksource to
allow high resolution timers and or dynamic ticks.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>

arch/x86_64/Kconfig

@@ -36,6 +36,10 @@ config GENERIC_CMOS_UPDATE
 	bool
 	default y
 
+config CLOCKSOURCE_WATCHDOG
+	bool
+	default y
+
 config ZONE_DMA32
 	bool
 	default y