drm/tegra: Changes for v4.16-rc1

The bulk of these changes are preparation work and addition of support
for Tegra186. Currently only HDMI output (the primary output on Jetson
TX2) is supported, but the hardware is also capable of doing DSI and
DisplayPort.

Tegra DRM now also uses the atomic commit helpers instead of the open-
coded variant that was only doing half its job. As a bit of a byproduct
of the Tegra186 support the driver also gained HDMI 2.0 as well as zpos
property support.

Along the way there are also a few patches to clean up a few things and
fix minor issues.

* tag 'drm/tegra/for-4.16-rc1-fixes' of git://anongit.freedesktop.org/tegra/linux: (51 commits)
  drm/tegra: dc: Properly cleanup overlay planes
  drm/tegra: dc: Fix possible_crtcs mask for planes
  drm/tegra: dc: Restore YUV overlay support
  drm/tegra: dc: Implement legacy blending
  drm/tegra: Correct timeout in tegra_syncpt_wait
  drm/tegra: gem: Correct iommu_map_sg() error checking
  drm/tegra: dc: Link DC1 to DC0 on Tegra20
  drm/tegra: Fix non-debugfs builds
  drm/tegra: dpaux: Keep reset defaults for hybrid pad parameters
  drm/tegra: Mark Tegra186 display hub PM functions __maybe_unused
  drm/tegra: Use IOMMU groups
  gpu: host1x: Use IOMMU groups
  drm/tegra: Implement zpos property
  drm/tegra: dc: Remove redundant spinlock
  drm/tegra: dc: Use direct offset to plane registers
  drm/tegra: dc: Support more formats
  drm/tegra: fb: Force alpha formats
  drm/tegra: dpaux: Add Tegra186 support
  drm/tegra: dpaux: Implement runtime PM
  drm/tegra: sor: Support HDMI 2.0 modes
  ...