The IEEE 802.15.4 drivers were compiled by default with debugging,
which caused them to be rather chatty and slow. This patch silences
them. People debugging drivers can still add a #define DEBUG in the
beginning of the respective file or use dynamic debug

This patch also removes the now unused option CONFIG_FFD.

Signed-off-by: Werner Almesberger <werner@almesberger.net>
Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>