sched/fair: Use throttled_csd_list for local unthrottle

sched/fair: Use throttled_csd_list for local unthrottle

When distribute_cfs_runtime() encounters a local cfs_rq, it adds it to a
local list and unthrottles it at the end, when it is done unthrottling
other cfs_rq(s) on cfs_b->throttled_cfs_rq until the bandwidth runs out.

Instead of using a local list, reuse the local CPU's
rq->throttled_csd_list and the __cfsb_csd_unthrottle() path for
unthrottle.

If this is the first cfs_rq to be queued on the "throttled_csd_list", it
prevents the need for a remote CPUs to interrupt this local CPU if they
themselves are performing async unthrottle.

If this is not the first cfs_rq on the list, there is an async unthrottle
operation pending on this local CPU and the unthrottle can be batched
together.

No functional changes intended.

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Benjamin Segall <bsegall@google.com>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260602050005.11160-3-kprateek.nayak@amd.com