drm/i915: parse backlight modulation frequency from the BIOS VBT

We don't actually do anything with the information yet, but parse and
log what's in the VBT.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/i915_drv.h
Simple merge

diff --cc drivers/gpu/drm/i915/intel_bios.c
Simple merge

diff --cc drivers/gpu/drm/i915/intel_bios.h
Simple merge