drm/xe: Use bookkeep slots for external BO's in exec IOCTL

drm/xe: Use bookkeep slots for external BO's in exec IOCTL

Fix external BO's dma-resv usage in exec IOCTL using bookkeep slots
rather than write slots. This leaves syncing to user space rather than
the KMD blindly enforcing write semantics on every external BO.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Kenneth Graunke <kenneth.w.graunke@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reported-by: Simona Vetter <simona.vetter@ffwll.ch>
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2673
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240911152622.903058-1-matthew.brost@intel.com
(cherry picked from commit b8b1163248759ba18509f7443a2d19b15b4c1df8)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>