drm/i915: Implement the intel_dp_autotest_edid function for DP EDID complaince tests

drm/i915: Implement the intel_dp_autotest_edid function for DP EDID complaince tests

Updates the EDID compliance test function to perform the analyze and react to
the EDID data read as a result of a hot plug event. The results of this
analysis are handed off to userspace so that the userspace app can set the
display mode appropriately for the test result/response.

The compliance_test_active flag now appears at the end of the individual
test handling functions. This is so that the kernel-side operations can
be completed without the risk of interruption from the userspace app
that is polling on that flag.

V2:
- Addressed mailing list feedback
- Removed excess debug messages
- Removed extraneous comments
- Fixed formatting issues (line length > 80)
- Updated the debug message in compute_edid_checksum to output hex values
  instead of decimal
V3:
- Addressed more list feedback
- Added the test_active flag to the autotest function
- Removed test_active flag from handler
- Added failsafe check on the compliance test active flag
  at the end of the test handler
- Fixed checkpatch.pl issues
V4:
- Removed the checksum computation function and its use as it has been
  rendered superfluous by changes to the core DRM EDID functions
- Updated to use the raw header corruption detection mechanism
- Moved the declaration of the test_data variable here
V5:
- Update test active flag variable name to match the change in the
  first patch of the series.
- Relocated the test active flag declaration and initialization
  to this patch
V6:
- Updated to use the new flag for raw EDID header corruption
- Removed the extra EDID read from the autotest function
- Added the edid_checksum variable to struct intel_dp so that the
  autotest function can write it to the sink device
- Moved the update to the hpd_pulse function to another patch
- Removed extraneous constants
V7:
- Fixed erroneous placement of the checksum assignment. In some cases
  such as when the EDID read fails and is NULL, this causes a NULL ptr
  dereference in the kernel. Bad news. Fixed now.
V8:
- Updated to support the kfree() on the EDID data added previously
V9:
- Updated for the long_hpd flag propagation
V10:
- Updated to use actual checksum from the EDID read that occurs during
  normal hot plug path execution
- Removed variables from intel_dp struct that are no longer needed
- Updated the patch subject to more closely match the nature and contents
  of the patch
- Fixed formatting problem (long line)
V11:
- Removed extra debug messages
- Updated comments to be more informative
- Removed extra variable
V12:
- Removed the 4 bit offset of the resolution setting in compliance data
- Changed to DRM_DEBUG_KMS instead of DRM_DEBUG_DRIVER

Signed-off-by: Todd Previte <tprevite@gmail.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>