drm/xe: Finish refactoring of exec_queue_create

drm/xe: Finish refactoring of exec_queue_create

Setting of exec_queue user extensions is moved from the end of the ioctl
function earlier, into __xe_exec_queue_alloc().
This fixes bug in that the USM attributes for access counters were being
applied too late, and effectively were ignored.

However, in order to apply user extensions this early, we can no longer
call q->ops functions.  Instead, make it more efficient. The user extension
functions can simply update the q->sched_props values and they will be
applied by the backend during q->ops->init().

v2: minor changes for readability (Matt)

Signed-off-by: Brian Welty <brian.welty@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>