altos: Get CC115L radio working.

altos: Get CC115L radio working.

This involved figuring out which GPIO signal would reliably indicate
that the transmitter was finished; I ended up using the PA_PD bit for
this.

This also converts all of the radio users to the long packet support
as the CC115L has only a 64-byte fifo, not large enough to hold either
an RDF tone or a regular AltOS telemetry packet.

This also renames the public API for sending APRS packets from
ao_radio_send_lots to ao_radio_send_aprs, which is at least more
accurate. The workings of that API haven't changed, just the name.

Signed-off-by: Keith Packard <keithp@keithp.com>