Add support for i915 I915_GEM_CREATE_EXT_SET_PAT on MTL

Merged Jordan Justen requested to merge jljusten/mesa:mtl-set-pat into main

This kernel extension to buffer creation allows userspace to select the PAT index to be used with the BO, which helps improve performance on MTL.

Also, thanks @currojerez and @kwg for helping track down a bug in the early version of the kernel patches!

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