ARM: vexpress: add sched_clock() for Versatile Express

Add a sched_clock() implementation to Versatile Express using the new
sched_clock() infrastructure for extending 32bit counters to full
64-bit nanoseconds.

Tested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 34311f4..17b5ff0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -268,6 +268,7 @@
 	select COMMON_CLKDEV
 	select GENERIC_CLOCKEVENTS
 	select HAVE_CLK
+	select HAVE_SCHED_CLOCK
 	select ICST
 	select PLAT_VERSATILE
 	help