New protocol decoder: nrf905

libsigrokdecode now supports yet another protocol decoder: nrf905.

This one stacks on top of the SPI decoder, and decodes the protocol of the Nordic Semiconductor nRF905 433/868/933MHz transceiver chip.

Some example traces are available in the sigrok-dumps repo and some test-cases in the sigrok-test repo, as usual.

The decoder was contributed by Jorge Solla Rubiales, thanks a lot!