intel/dev: Add mem information (regions from kernel or a fallback)

@llandwerlin: Here's a subset of !16739 (merged), which doesn't depend on the kernel uapi change.

I did some renaming here based on your lack-of-regions "fallback" support. First, devinfo::regions is changed to devinfo::mem, since it's valid info aside from regions. Second, I renamed the "valid" field to "use_class_instance" to indicate that the mem_class & mem_instance fields can/should be used.

I didn't get a chance to run CI yet, but I did some piglit & crucible testing on ADL and DG2. I'll try to get some CI testing done tomorrow.

If you are ok with the renames above, I can take the rest of the !16739 (merged) patches and provide a reworked branch.