drm/xe/migrate: Allow xe_migrate_vram() also on non-pagefault capable devices

The drm_pagemap functionality does not depend on the device having
recoverable pagefaults available. So allow xe_migrate_vram() also for
such devices. Even if this will have little use in practice, it's
beneficial for testin multi-device SVM, since a memory provider could
be a non-pagefault capable gpu.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250326080551.40201-5-thomas.hellstrom@linux.intel.com