drm/i915: re-layout intel_panel.c to obey 80 char limit

drm/i915: re-layout intel_panel.c to obey 80 char limit

Especially intel_gmch_panel_fitting was shifting way too much over the
right edge and also was way too long. So extract two helpers, one for
gen4+ and one for gen2/3. Now the entire thing is again almost
readable ...

Spurred by checkpatch freaking out about a Ville's pipeconfig rework
in intel_panel.c

Otherwise just two lines that needed appropriate breaking.

Not functional change in this patch.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>