ACPI / sleep: Introduce CONFIG_ACPI_SYSTEM_POWER_STATES_SUPPORT

ACPI 5.1 does not currently support S states for ARM64 hardware but
ACPI code will call acpi_target_system_state() and acpi_sleep_init()
for device power management, so introduce
CONFIG_ACPI_SYSTEM_POWER_STATES_SUPPORT and select it for x86 and
ia64 only to make sleep functions available, and also introduce stub
function to allow other drivers to function until S states are defined
for ARM64.

It will be no functional change for x86 and IA64.

Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Graeme Gregory <graeme.gregory@linaro.org>
Signed-off-by: Tomasz Nowicki <tomasz.nowicki@linaro.org>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index 623b117..db153c6 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -23,7 +23,7 @@
 
 # Power management related files
 acpi-y				+= wakeup.o
-acpi-y				+= sleep.o
+acpi-$(CONFIG_ACPI_SYSTEM_POWER_STATES_SUPPORT) += sleep.o
 acpi-y				+= device_pm.o
 acpi-$(CONFIG_ACPI_SLEEP)	+= proc.o