staging: wfx: add support for tx_power_loop

During the calibration of the RF amplifier, the device is able to provide
some data about the status of the amplifier.

Record these data and expose them in debugfs.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200526171821.934581-5-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>