We're seeing a lot of bogus backlight interfaces on newer machines without
a LCD such as desktops, servers and HDMI sticks. This causes userspace to
show a non-functional brightness slider in e.g. the GNOME3 system menu,
which is undesirable. And, in general, we should simply just not register
a non functional backlight interface.

Checking the LCD flag causes the bogus acpi_video backlight interfaces to
go away (on the machines this was tested on).

This change sets the lcd_only option by default on any machines which
are Win8-ready, to fix this.

This is not entirely without a risk of regressions, but video_detect.c
already prefers native-backlight interfaces over the acpi_video one
on Win8-ready machines, calling acpi_video_unregister_backlight() as soon
as a native interface shows up. This is done because the ACPI backlight
interface often is broken on Win8-ready machines, because win8 does not
seem to actually use it.

So in practice we already end up not registering the ACPI backlight
interface on (most) Win8-ready machines with a LCD panel, thus this
change does not change anything for (most) machines with a LCD panel
and on machines without a LCD panel we actually don't want to register
any backlight interfaces.

This has been tested on the following machines and fixes a bogus backlight
interface showing up there:
 - Desktop with an Asrock B150M Pro4S/D3 m.b. using i5-6500 builtin gfx
 - Intel Compute Stick STK1AW32SC
 - Meegopad T08 HDMI stick

Bogus backlight interfaces have also been reported on:
 - Desktop with Asus H87I-Plus m.b.
 - Desktop with ASRock B75M-ITX m.b.
 - Desktop with Gigabyte Z87-D3HP m.b.
 - Dell PowerEdge T20 desktop

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1097436
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1133327
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1133329
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1133646


Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>