drm/i914: s/l_info/dimm_l/ etc.

Rename the dimm info structs for clarity.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190306203551.24592-10-ville.syrjala@linux.intel.com