[Intel-gfx] Add support for Displayport CTS 4.2.2.7, 4.2.2.8 and 4.2.2.9

[Todd Previte]

Three patches to add support for the above-mentioned compliance tests. The 
first two are branch device tests and the third is a 4-block E-DDC read.     

Todd Previte (3)
   drm/i915: Displayport compliance test 4.2.2.8 support
   drm/i915: Displayport compliance test 4.2.2.7 support
   drm/i915: Displayport compliance test 4.2.2.9 support


drivers/gpu/drm/i915/intel_dp.c  | 30 ++++++++++++++++++++++++++++--
drivers/gpu/drm/i915/intel_drv.h |  4 ++++
2 files changed, 32 insertions(+), 2 deletions(-)