arch/nrf52: add initial support for IEEE 802.15.4
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
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