Add wrapper function around RB tree to determine if i915_sched_engine is
empty.
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210618010638.98941-3-matthew.brost@intel.com