sched: Convert paravirt_steal to new static key APIs

paravirt_steal_rq_enabled and paravirt_steal_enabled use raw static_key
APIs which are now deprecated. Use the new API instead.

No functional change.

Signed-off-by: Hongyan Xia <hongyan.xia@transsion.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juergen Gross <jgross@suse.com>
Link: https://patch.msgid.link/20260819081207.12150-1-hongyan.xia@transsion.com