Cleaned up interrupt handling in atspi-txrx. Report ED. Shut down at end.
Cleaned up interrupt handling in atspi-txrx. Report ED. Shut down at end.

- tools/atspi-txrx/atspi-txrx.c (receive, wait_for_interrupt): moved wait
  for interrupt logic to separate function and made it more versatile
- tools/atspi-txrx/atspi-txrx.c (init_txrx, receive): clear interrupts in
  init_txrx now, so that also transmit has a clear interrupt register
- tools/atspi-txrx/atspi-txrx.c (set_channel): since we're in TRX_OFF,
  don't wait for PLL lock
- tools/atspi-txrx/atspi-txrx.c (receive): wait for PLL lock interrupt
  after activating receiver
- tools/atspi-txrx/atspi-txrx.c (transmit): wait for PLL lock interrupt
  after activating the PLL
- tools/atspi-txrx/atspi-txrx.c (transmit): wait for TRX_END interrupt
  after sending a frame
- tools/atspi-txrx/atspi-txrx.c (receive): report the Energy Density (ED)
  after receiving a frame
- tools/atspi-txrx/atspi-txrx.c (main): shut down the board with
  atspi_close, so that we can hot-swap safely

cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan