drm/ttm: Add ttm_bo_access

drm/ttm: Add ttm_bo_access

Non-contiguous VRAM cannot easily be mapped in TTM nor can non-visible
VRAM easily be accessed. Add ttm_bo_access, which is similar to
ttm_bo_vm_access, to access such memory.

v4:
 - Fix checkpatch warnings (CI)
v5:
 - Fix checkpatch warnings (CI)
v6:
 - Fix kernel doc (Auld)
v7:
 - Move ttm_bo_access to ttm_bo_vm.c (Christian)

Cc: Christian König <christian.koenig@amd.com>
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>
Tested-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241126174615.2665852-3-matthew.brost@intel.com