Adds up to 8 TXT buffers (number of TXT buffers now defined by generic from 2 - 8).
Adds TXTB_INFO which allows querying buffer count from HW.
Adds RETR_CTR which allows getting current value of retransmitt counter.
Adds MODE[TTTM] - Time triggered mode
Adds MODE[ROM] - Restricted operation mode
Adds MODE[RXBAM] - RX buffer automatic mode, side-effect +1 increment on RX buffer
                   read pointer by read from RX_DATA>