rbtree, sched/fair: Use rb_add_cached()

mainline inclusion
from mainline-v5.12-rc1
commit bf9be9a1
category: feature
feature: SPR PMU uncore support
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I5BECO



Intel-SIG: commit bf9be9a1 rbtree, sched/fair: Use rb_add_cached()
This commit is backported as a dependency for SPR PMU uncore support.

-------------------------------------

Reduce rbtree boiler plate by using the new helper function.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Yunying Sun <yunying.sun@intel.com>
Signed-off-by: Aichun Shi <aichun.shi@intel.com>