drm/i915: Get panel_type from OpRegion panel details

We've had problems on several occasions with using the panel type
from the VBT block 40. Usually it seems to be 2, which often
doesn't give us the correct timings for the panel. After some
more digging I found a way to get a panel type via the OpRegion
SWSCI GBDA "Get Panel Details" method. Let's try to use it.

The spec has this to say about the output:
"Bits [15:8] - Panel Type
 Bits contain the panel type user setting from CMOS
 00h = Not Valid, use default Panel Type & Timings from VBT
 01h - 0Fh = Panel Number"

Another version of the spec lists the valid range as 1-16, which makes
more sense since VBT supports 16 panels. Based on actual results
from Rob's G45, 1-16 is what we need to accept.

The other bits in the output don't look relevant for the problem at
hand.

The input is specified as:
"Bits [31:4] - Reserved
 Reserved (must be zero)
 Bits [3:0] - Panel Number
 These bits contain the sequential index of Panel, starting at 0 and
 counting upwards from the first integrated Internal Flat-Panel Display
 Encoder present, and then from the first external Display Encoder
 (e.g., S/DVO-B then S/DVO-C) which supports Internal Flat-Panels.
 0h - 0Fh = Panel number"

For now I've just hardcoded the input panel number as 0. That would seem
like a decent choise for LVDS. Not so sure about eDP when port != A.

v2: Accept values 1-16
    Filter out bogus results in opregion code (Jani)
    Add debug logging for all the different branches (Jani)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rob Kramer <rob@solution-space.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94825


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460359431-11003-1-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: Rob Kramer <rob@solution-space.com>