ACPI: PM: Silence missing prototype warning

Silence the following warning when built with W=1:

 | CC   drivers/acpi/device_pm.c
 |      warning: no previous prototype for function 'acpi_subsys_restore_early' [-Wmissing-prototypes]
 |              int acpi_subsys_restore_early(struct device *dev)
 |                  ^

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/acpi.h

@@ -1136,6 +1136,7 @@ int acpi_subsys_freeze(struct device *dev);
 int acpi_subsys_poweroff(struct device *dev);
 void acpi_ec_mark_gpe_for_wake(void);
 void acpi_ec_set_gpe_wake_mask(u8 action);
+int acpi_subsys_restore_early(struct device *dev);
 #else
 static inline int acpi_subsys_prepare(struct device *dev) { return 0; }
 static inline void acpi_subsys_complete(struct device *dev) {}
@@ -1144,6 +1145,7 @@ static inline int acpi_subsys_suspend_noirq(struct device *dev) { return 0; }
 static inline int acpi_subsys_suspend(struct device *dev) { return 0; }
 static inline int acpi_subsys_freeze(struct device *dev) { return 0; }
 static inline int acpi_subsys_poweroff(struct device *dev) { return 0; }
+static inline int acpi_subsys_restore_early(struct device *dev) { return 0; }
 static inline void acpi_ec_mark_gpe_for_wake(void) {}
 static inline void acpi_ec_set_gpe_wake_mask(u8 action) {}
 #endif