drm/i915: Force DPCD backlight mode for BOE 2270 panel

BOE 2270 panel failed to control backlight brightness.
Add it in edid quirks to force using DPCD backlight control.
Then the brightness can be controlled.

Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201009085750.88490-2-aaron.ma@canonical.com