mac80211/cfg80211: move wiphy specific debugfs entries to cfg80211

This moves the cfg80211 specific stuff to new cfg80211 debugfs
entries. Non-mac80211 will also get these entries now. There were
only 4 which we take:

rts_threshold
fragmentation_threshold
short_retry_limit
long_retry_limit

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>