Draft: Support i915 forked Linux uapi for DG2

i915 has a forked Linux uapi documented at: https://github.com/intel-gpu/drm-uapi-helper (See i915_drm_prelim.h)

These patches won't be merged to Mesa upstream, but show how Anvil and Iris can make use of the interfaces.

This MR also includes patches from !12706 (merged), !13866 (merged) and !14511 (merged) to allow the patches to apply & build.