timer: vt8500: Move timer code to drivers/clocksource

This patch moves arch-vt8500/timer.c into drivers/clocksource and
updates the necessary Kconfig/Makefile options.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index a32b7a9..7d978c1 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -28,6 +28,9 @@
 config SUNXI_TIMER
 	bool
 
+config VT8500_TIMER
+	bool
+
 config CLKSRC_NOMADIK_MTU
 	bool
 	depends on (ARCH_NOMADIK || ARCH_U8500)