drm/tegra: Changes for v4.17-rc1

This fixes mmap() for fbdev devices by providing a custom implementation
based on the KMS variant. This is a fairly exotic case these days, hence
why it is not flagged for stable.

There is also support for dedicating one of the overlay planes to serve
as a hardware cursor on older Tegra that did support hardware cursors
but not RGBA formats for it.

Planes will now also export the IN_FORMATS property by supporting the
various block-linear tiling modifiers for RGBA pixel formats.

Other than that, there's a bit of cleanup of DMA API abuse, use of the
private object infrastructure for global state (rather than subclassing
atomic state objects) and an implementation of ->{begin,end}_cpu_access
callbacks for PRIME exported buffers, which allow users to perform cache
maintenance on these buffers.

* tag 'drm/tegra/for-4.17-rc1' of git://anongit.freedesktop.org/tegra/linux:
  drm/tegra: prime: Implement ->{begin,end}_cpu_access()
  drm/tegra: gem: Map pages via the DMA API
  drm/tegra: hub: Use private object for global state
  drm/tegra: fb: Properly support linear modifier
  drm/tegra: plane: Support format modifiers
  drm/tegra: dc: Dedicate overlay plane to cursor on older Tegra's
  drm/tegra: plane: Make tegra_plane_get_overlap_index() static
  drm/tegra: fb: Implement ->fb_mmap() callback
  drm/tegra: gem: Make __tegra_gem_mmap() available more widely
  drm/tegra: gem: Reshuffle declarations