video driver in acpi_backlight=vendor mode.

Issuing these events is the right thing to do, and will work around
bugzilla #13368, if userspace is properly configured and actively
handles these events.

For other ThinkPads, and when ACPI video is handling brightness
changes, thinkpad-acpi will continue NOT sending KEY_BRIGHTNESS*
events by default.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>
V