sched_ext: scx_qmap: Reset a child's cpuperf targets once its PERF revoke takes effect

A child that ran a cid at a low cpuperf target leaves the target there when
PERF is revoked, since the kernel resets targets only at root enable. Reset
it to SCX_CPUPERF_ONE from ops.sub_child_ecaps_updated() once the revoke is
in effect, a detach included. Count the deliveries in the hier stats.

Signed-off-by: Tejun Heo <tj@kernel.org>