ieee802154: move wpan-phy.h to cfg802154.h

The wpan-phy header contains the wpan_phy struct information. Later this
header will be have similar function like cfg80211 header. The cfg80211
header contains the wiphy struct which is identically the wpan_phy
struct inside 802.15.4 subsystem.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Cc: Alan Ott <alan@signal11.us>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>