drm/xe/bmg: fix compressed VRAM handling

drm/xe/bmg: fix compressed VRAM handling

There looks to be an issue in our compression handling when the BO pages
are very fragmented, where we choose to skip the identity map and
instead fall back to emitting the PTEs by hand when migrating memory,
such that we can hopefully do more work per blit operation. However in
such a case we need to ensure the src PTEs are correctly tagged with a
compression enabled PAT index on dgpu xe2+, otherwise the copy will
simply treat the src memory as uncompressed, leading to corruption if
the memory was compressed by the user.

To fix this pass along use_comp_pat into emit_pte() on the src side, to
indicate that compression should be considered.

v2 (Jonathan): tweak the commit message

Fixes: 523f191cc0c7 ("drm/xe/xe_migrate: Handle migration logic for xe2+ dgfx")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Akshata Jahagirdar <akshata.jahagirdar@intel.com>
Cc: <stable@vger.kernel.org> # v6.12+
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://lore.kernel.org/r/20250701103949.83116-2-matthew.auld@intel.com