ACPI: video: Allow selecting NVidia-WMI-EC or Apple GMUX backlight from the cmdline

ACPI: video: Allow selecting NVidia-WMI-EC or Apple GMUX backlight from the cmdline

commit 420a1116aef0e8e12c305508f45ce73e5ae30a09 upstream.

The patches adding NVidia-WMI-EC and Apple GMUX backlight detection
support to acpi_video_get_backlight_type(), forgot to update
acpi_video_parse_cmdline() to allow manually selecting these from
the commandline.

Add support for these to acpi_video_parse_cmdline().

Fixes: 9a57294ea4b6 ("ACPI: video: Add Nvidia WMI EC brightness control detection (v3)")
Fixes: 5e21c1bca3e8 ("ACPI: video: Add Apple GMUX brightness control detection")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>