staging: wfx: add I/O API

hwio.c provides an abstraction to access different types of register of
the chip.

Note that only data register (aka FRAME_OUT) and control register are
used normal communication. Other registers are only used during chip
start up.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20190919142527.31797-4-Jerome.Pouiller@silabs.com


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