drm/xe: Only allow 1 ufence per exec / bind IOCTL

drm/xe: Only allow 1 ufence per exec / bind IOCTL

The way exec ufences are coded only 1 ufence per IOCTL will be signaled.
It is possible to fix this but for current use cases 1 ufence per IOCTL
is sufficient. Enforce a limit of 1 ufence per IOCTL (both exec and bind
to be uniform).

v2:
- Add fixes tag (Thomas)

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Brian Welty <brian.welty@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240124234413.1640825-1-matthew.brost@intel.com