intel: small BAR preparation patches
The i915 small BAR uapi is now in drm-tip, but not yet in the main drm tree. These patches rework iris and anvil to prepare for using the uapi.
These patches mostly exist in @llandwerlin's !16739 (merged) MR, so this MR will merge some of the preparation work for that MR.
The remaining patches for !16739 (merged) are rebased on these patches in https://gitlab.freedesktop.org/jljusten/mesa/-/commits/small-bar.