cfg80211: support creating wiphy with suggested name

Kernel will attempt to use the name if it is supplied,
but if name cannot be used for some reason, the default
phyX name will be used instead.

Signed-off-by: Ben Greear <greearb@candelatech.com>
[while at it, use wiphy_name() instead of dev_name(),
 fix format string issue reported by Kees Cook]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>