crda: add support to send DFS master region

wireless-regdb now has support for a DFS master region
for each country. We must read this from the file and
send it as an NL80211_ATTR_DFS_REGION attribute.

We add a "creqs" value for the country structure but only
use the first two bits as that is all we need right now.

Signed-off-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>