arm64: kernel: add PM build infrastructure

This patch adds the required makefile and kconfig entries to enable PM
for arm64 systems.

The kernel relies on the cpu_{suspend}/{resume} infrastructure to
properly save the context for a CPU and put it to sleep, hence this
patch adds the config option required to enable cpu_{suspend}/{resume}
API.

In order to rely on the CPU PM implementation for saving and restoring
of CPU subsystems like GIC and PMU, the arch Kconfig must be also
augmented to select the CONFIG_CPU_PM option when SUSPEND or CPU_IDLE
kernel implementations are selected.
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

arch/arm64/Kconfig

@@ -12,6 +12,7 @@ config ARM64
 	select BUILDTIME_EXTABLE_SORT
 	select CLONE_BACKWARDS
 	select COMMON_CLK
+	select CPU_PM if (SUSPEND || CPU_IDLE)
 	select GENERIC_CLOCKEVENTS
 	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
 	select GENERIC_IOMAP
@@ -277,6 +278,18 @@ config SYSVIPC_COMPAT
 
 endmenu
 
+menu "Power management options"
+
+source "kernel/power/Kconfig"
+
+config ARCH_SUSPEND_POSSIBLE
+	def_bool y
+
+config ARM64_CPU_SUSPEND
+	def_bool PM_SLEEP
+
+endmenu
+
 source "net/Kconfig"
 
 source "drivers/Kconfig"

arch/arm64/kernel/Makefile

@@ -18,6 +18,7 @@ arm64-obj-$(CONFIG_SMP)			+= smp.o smp_spin_table.o
 arm64-obj-$(CONFIG_HW_PERF_EVENTS)	+= perf_event.o
 arm64-obj-$(CONFIG_HAVE_HW_BREAKPOINT)+= hw_breakpoint.o
 arm64-obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
+arm64-obj-$(CONFIG_ARM64_CPU_SUSPEND)	+= sleep.o suspend.o
 
 obj-y					+= $(arm64-obj-y) vdso/
 obj-m					+= $(arm64-obj-m)