[Quantal] [Precise SRU] drm/radeon: fix unintended display toggles

[Alex Hung]

SRU Justification:

Impact:
  An additional KEY_SWITCHVIDEOMODE keycode is sent with when
  brightness up/down hotkey are pressed on some systems with AMD's
  VGA chips. It toggles displays unintendedly when multiple monitors
  are connected or causes LCD panel flickers with no external monitors.

Fix:
  The standard video events may be overloaded for device specific
  purposes. For example AMD ACPI interface overloads
  ACPI_VIDEO_NOTIFY_PROBE (0x81) to signal AMD-specific events.
  This patch gives the handlers the chance to examine the event and
  block the keypress if the event is device specific.

Test:
  I tested on ASUS 1015U, and it removed the additional keycode.

Note:
  The patches are included in upstream, but it is needed to be included
  in precise lts-backport-quantal and quantal kernels:

  92fdf89aa95de32dba1cb44fe7f5c54824b4b2c4
  8a37c65df9dcbd1c891df2b4a94157999b654841

  A number of previous commits are also required:

  c49170742d6928b16fb3839b47a94cc41630dbe0
  fda4b25c55a59ba12378e4b9e4553f6ea57d802d
  ce3cf821a31f9824eda788cbd3e710d8047e82df
  fd64ca8a9d9d7e92fc81fe0b23dcf324246fd356
  86504672f7d79986a8ef618fb120044220e3d1eb
  f3728734ba78310525bf4a361c7787c7c6fa5d40
  910308802c528f8afe864b694d5456fedd0bb18f
  af7912e57316caa1b705f06b03592cec0737cb36
  efd4e418f2bb8a8b21f96fd44e775eaf6dd55905
  9e05b2f49eb9484e857e9b6c70dea3bbbe564290

BugLink: http://bugs.launchpad.net/bugs/1110219