drm/i915: Add missing MacBook Pro models with dual channel LVDS

Single channel LVDS maxes out at 112 MHz. The 15" pre-retina models
shipped with 1440x900 (106 MHz) by default or 1680x1050 (119 MHz)
as a BTO option, both versions used dual channel LVDS even though
the smaller one would have fit into a single channel.

Notes:
  Bug report showing that the MacBookPro8,2 with 1440x900 uses dual
  channel LVDS (this lead to it being hardcoded in intel_lvds.c by
  Daniel Vetter with commit 618563e3945b9d0864154bab3c607865b557cecc):
    https://bugzilla.kernel.org/show_bug.cgi?id=42842

  If i915.lvds_channel_mode=2 is missing even though the machine needs
  it, every other vertical line is white and consequently, only the left
  half of the screen is visible (verified by myself on a MacBookPro9,1).

  Forum posting concerning a MacBookPro6,2 with 1440x900, author is
  using i915.lvds_channel_mode=2 on the kernel command line, proving
  that the machine uses dual channels:
    https://bbs.archlinux.org/viewtopic.php?id=185770

  Chi Mei N154C6-L04 with 1440x900 is a replacement panel for all
  MacBook Pro "A1286" models, and that model number encompasses the
  MacBookPro6,2 / 8,2 / 9,1. Page 17 of the panel's datasheet shows it's
  driven with dual channel LVDS:
    http://www.ebay.com/itm/-/400690878560
    http://www.everymac.com/ultimate-mac-lookup/?search_keywords=A1286
    http://www.taopanel.com/chimei/datasheet/N154C6-L04.pdf

  Those three 15" models, MacBookPro6,2 / 8,2 / 9,1, are the only ones
  with i915 graphics and dual channel LVDS, so that list should be
  complete. And the 8,2 is already in intel_lvds.c.

  Possible motivation to use dual channel LVDS even on the 1440x900
  models: Reduce the number of different parts, i.e. use identical logic
  boards and display cabling on both versions and the only differing
  component is the panel.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org
[Jani: included notes in the commit message for posterity]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

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