wifi: mac80211: move ps setting to vif config

This really shouldn't be in a per-link config, we don't want
to let anyone control it that way (if anything, link powersave
could be forced through APIs to activate/deactivate a link),
and we don't support powersave in software with devices that
can do MLO.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>