staging: wfx: setup initial chip configuration

staging: wfx: setup initial chip configuration

A few tasks remain to be done in order to finish chip initial
configuration:
   - configure chip to use multi-tx confirmation (speed up data
     transfer)
   - configure chip to use wake-up feature (save power consumption
     during runtime)
   - set hardware configuration (clocks, RF, pinout, etc...) using a
     Platform Data Set (PDS) file

On release, driver completely shutdown the chip to save power
consumption.

Documentation about PDS and PDS data for sample boards are available
here[1]. One day, PDS data may find a place in device tree but,
currently, PDS is too much linked with firmware to allowing that.

This patch also add "send_pds" file in debugfs to be able to dynamically
change PDS (only for debug, of course).

[1]: https://github.com/SiliconLabs/wfx-firmware/tree/master/PDS

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20190919142527.31797-15-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>