acpi_lid: add an in-kernel lid state eventhandler

Lid state changes are only published to userland, via devd and evdev.
Drivers that need to react to the lid in the kernel have no hook, so
they end up installing a second ACPI_DEVICE_NOTIFY handler on the same
lid object and reimplementing the _LID evaluation.

Add acpi_lid_event, invoked from acpi_lid_status_update() alongside the
existing devd notification, carrying the new state (1 open, 0 closed).

Reviewed by:	adrian
Differential Revision:	https://reviews.freebsd.org/D60704

sys/dev/acpica/acpi_lid.c

@@ -117,6 +117,9 @@ acpi_lid_status_update(struct acpi_lid_softc *sc)
 	/* Send notification via devd */
 	acpi_UserNotify("Lid", sc->lid_handle, sc->lid_status);
 
+	/* Notify in-kernel consumers */
+	EVENTHANDLER_INVOKE(acpi_lid_event, sc->lid_status);
+
 #ifdef EVDEV_SUPPORT
 	/* Notify evdev about lid status */
 	evdev_push_sw(sc->lid_evdev, SW_LID, lid_status ? 0 : 1);

sys/dev/acpica/acpivar.h

@@ -456,6 +456,11 @@ EVENTHANDLER_DECLARE(acpi_video_event, acpi_event_handler_t);
 EVENTHANDLER_DECLARE(acpi_post_dev_suspend, acpi_event_handler_t);
 EVENTHANDLER_DECLARE(acpi_pre_dev_resume, acpi_event_handler_t);
 
+/* Lid state changes.  The int argument is 1 for open, 0 for closed. */
+typedef void (*acpi_lid_event_handler_t)(void *, int);
+
+EVENTHANDLER_DECLARE(acpi_lid_event, acpi_lid_event_handler_t);
+
 void		acpi_invoke_sleep_eventhandler(const enum power_stype *stype);
 void		acpi_invoke_wake_eventhandler(const enum power_stype *stype);