drm/xe: Add xe_ttm_access_memory

drm/xe: Add xe_ttm_access_memory

Non-contiguous VRAM cannot easily be mapped in TTM nor can non-visible
VRAM easily be accessed. Add xe_ttm_access_memory which hooks into
ttm_bo_access to access such memory.

v4:
 - Assert memory access rather than taking RPM ref (Thomas / Auld)
 - Fix warning on xe_res_cursor.h for non-zero offset (Mika)

Reported-by: Christoph Manszewski <christoph.manszewski@intel.com>
Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241126174615.2665852-4-matthew.brost@intel.com