[RFC libdrm] intel: Softpin support

[Michał Winiarski]

The goal of this series is to start a discussion whether the interface and
implementation of softpin support proposed for libdrm is acceptable by all
interested parties.
The i915 patches are added so that it's easy to apply the series on latest
drm-intel-nightly and libdrm master and start using softpin.

Michał Winiarski (1):
  drm/i915/gtt: Allow adventurous users to select enable_ppgtt=3
is not strictly necessary for softpin itself, but it is needed for SVM usecase.

Chris Wilson (1):
  drm/i915: Add soft-pinning API for execbuffer
is just v5 from Thomas Daniel rebased on top of current nightly.