arm64: enable generic clockevent broadcast

On platforms with power management capabilities, timers that are shut
down when a CPU enters deep C-states must be emulated using an always-on
timer and a timer IPI to relay the timer IRQ to target CPUs on an SMP
system.

This patch enables the generic clockevents broadcast infrastructure for
arm64, by providing the required Kconfig entries and adding the timer
IPI infrastructure.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6d4dd22..baab4eb 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -2,6 +2,7 @@
 	def_bool y
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select ARCH_USE_CMPXCHG_LOCKREF
+	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_WANT_OPTIONAL_GPIOLIB
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 	select ARCH_WANT_FRAME_POINTERS
@@ -12,6 +13,7 @@
 	select CLONE_BACKWARDS
 	select COMMON_CLK
 	select GENERIC_CLOCKEVENTS
+	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
 	select GENERIC_IOMAP
 	select GENERIC_IRQ_PROBE
 	select GENERIC_IRQ_SHOW