libbladeRF: Re-enable transmit and receive.

Call the vendor commands to get RX and TX flowing, like at the
end of the FPGA programming routine.
libbladeRF: Add API to change the ADC sampling location.

The ADC can be configured to sample from the internal inputs
or from the external pins.  Adding the API to change the sampling
between internal and external.  Also using the appropriate API
function for the CLI.
Merge remote-tracking branch 'upstream/master'