drm/i915/lvds: separate border enable readout from panel fitter

The LVDS border enable is independent from the panel fitter. Move the
readout of the "border bits" from i9xx_get_pfit_config() to
intel_lvds_get_config(), where it will be read if LVDS is enabled even
if the panel fitter is not.

This fixes the state checker warning:

[drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in
gmch_pfit.lvds_border_bits (expected 0x00008000, found 0x00000000)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: drm-intel-fixes@lists.freedesktop.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=87632


Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461933243-2140-1-git-send-email-jani.nikula@intel.com