ACPI: don't duplicate input events on netlink

The previous events patch added a netlink event for every
user of the legacy /proc/acpi/event interface.

However, some users of /proc/acpi/event are really input events,
and they already report their events via the input layer.

Introduce a new interface, acpi_bus_generate_netlink_event(),
which is explicitly called by devices that want to repoprt
events via netlink.  This allows the input-like events
to opt-out of generating netlink events.  In summary:

events that are sent via netlink:
	ac/battery/sbs
	thermal
	processor
	thinkpad_acpi dock/bay

events that are sent via input layer:
	button
	video hotkey
	thinkpad_acpi hotkey
	asus_acpi/asus-laptop hotkey
	sonypi/sonylaptop

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>