[PATCH v2 0/5] VRAM health check + CCS fix

[Matthew Auld <matthew.auld@intel.com>]

Add a basic VRAM health check routine, which does some basic sanity
checking on the last VRAM page. This could be extended in the future.
This seems to reproduce the same CCS issue as Linus, on my b570.

This also picks up the fix from Linus. I went with leaving it as-is,
but that means we need to fixup the identity mapping to support 4K
pages for the tail part of usable VRAM.

It doesn't look like anything in our CI actually has the CCS alignment
issue present, so merging the fix from Linus without the identity map
changes likely shouldn't trigger any asserts, if that does end up
coming in via another tree, AFAICT.

v2:
 - Give more details around what the VRAM health check actually does
   and how it catches the CCS bug (Matt B).
 - Tweak the CCS base + alignment print (Matt B).
 - Drop the fix from Linus; this is now already in drm-tip.
 - Add some hardening for VRAM CPU mapping also.

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2.55.0