ACPI / hotplug / PCI: Define hotplug context lock in the core

Subsequent changes will require the ACPI core to acquire the lock
protecting the ACPIPHP hotplug contexts, so move the definition of
the lock to the core and change its name to be more generic.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>

include/acpi/acpi_bus.h

@@ -404,6 +404,8 @@ static inline bool acpi_bus_can_wakeup(acpi_handle handle) { return false; }
 
 void acpi_scan_lock_acquire(void);
 void acpi_scan_lock_release(void);
+void acpi_lock_hp_context(void);
+void acpi_unlock_hp_context(void);
 int acpi_scan_add_handler(struct acpi_scan_handler *handler);
 int acpi_bus_register_driver(struct acpi_driver *driver);
 void acpi_bus_unregister_driver(struct acpi_driver *driver);