sched_deadline, docs: add affinity setting with cgroup2 cpuset controller

sched_deadline, docs: add affinity setting with cgroup2 cpuset controller

Setting the cpu affinity mask of a SCHED_DEADLINE process using the cgroup v1
cpuset controller is already detailed. Add similar information for cgroup v2's
cpuset controller.

Signed-off-by: Shashank Balaji <shashank.mahadasyam@sony.com>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250527-sched-deadline-cpu-affinity-v2-2-b8b40a4feefa@sony.com