- remove read-write logic - this should be handled by radio protocol implementation
- remove EVENTS and TASKS bit definitions - we can just use a signle definition
- add more radio ops
- fix frequency configuration
- fix printf warnings
- fix radio reset

Supported features:

- frame transmition
- frame reception and filtering
- immediate ACK (incoming and outgoing)
- promiscuous mode
- delayed transmision
- radio events trace
- setting pending bit for all incoming Data Request frames
- un-slotted CSMA-CA

Work in progres features (some logic is present, but they require more work):

- beacon transmision (periodic transmition works, but requires verification)
- slotted CSMA-CA
- GTS

Fetures not implemented:

- enhanced ACK (Enh-ACK)
- enhanced beacon
- low power mode
- advanced features from IEEE 802.15.4e (DSME, TSCH)

Added examples for boards:

- nrf52832-dk: mrf24j40_6lowpan
- nrf52832-dk: mrf24j40_mac
- nrf52840-dk: ieee802154_6lowpan
- nrf52840-dk: ieee802154_mac
- nrf52840-dongle: ieee802154_mac
- nrf9160-dk-nrf52: ieee802154_6lowpan
- nrf9160-dk-nrf52: ieee802154_mac