drm/xe: Add ops_execute function which returns a fence

Add ops_execute function which returns a fence. This will be helpful to
initiate all binds (VM bind IOCTL, rebinds in exec IOCTL, rebinds in
preempt rebind worker, and rebinds in pagefaults) via a gpuva ops list.
Returning a fence is needed in various paths.

v2:
 - Rebase

Cc: Oak Zeng <oak.zeng@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Oak Zeng <oak.zeng@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240425045513.1913039-3-matthew.brost@intel.com