basic *build* support of gen12 for iris and anvil

This patchset adopts gen11 code to build basic gen12 support into iris and anvil. (i965 will not support gen12.) Over time, future patchsets will add the various changes needed to support gen12.

Edit: pci-ids and INTEL_DEBUG=alpha were dropped

Since the driver will not yet work on real gen12 hardware, I added an INTEL_DEBUG=alpha flag to help notify users that the support in this branch in not ready. The drivers will not start for gen12 unless that environment variable debug flag is set.

About the only thing that will work on gen12 hardware with this patchset is running wflinfo. For example, this command works:

INTEL_DEBUG=alpha wflinfo -p gbm -a gl

On any system with intel graphics you can also override the driver to iris and device to tgl to get a similar output:

MESA_LOADER_DRIVER_OVERRIDE=iris INTEL_DEVID_OVERRIDE=tgl INTEL_DEBUG=alpha wflinfo -p gbm -a gl