ARM: local timers: Add A15 architected timer support

Add support for the A15 generic timer and clocksource.
As the timer generates interrupts on a different PPI depending
on the execution mode (normal or secure), it is possible to
register two different PPIs.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index cf006d4..4faabba 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1543,6 +1543,12 @@
 	help
 	  This option enables support for the ARM system coherency unit
 
+config ARM_ARCH_TIMER
+	bool "Architected timer support"
+	depends on CPU_V7
+	help
+	  This option enables support for the ARM architected timer
+
 config HAVE_ARM_TWD
 	bool
 	depends on SMP