cfg80211: allow multiple driver regulatory_hints()

We add support for multiple drivers to provide a regulatory_hint()
on a system by adding a wiphy specific regulatory domain cache.
This allows drivers to keep around cache their own regulatory domain
structure queried from CRDA.

We handle conflicts by intersecting multiple regulatory domains,
each driver will stick to its own regulatory domain though unless
a country IE has been received and processed.

If the user already requested a regulatory domain and a driver
requests the same regulatory domain then simply copy to the
driver's regd the same regulatory domain and do not call
CRDA, do not collect $200.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>