staging: wfx: introduce a way to poll IRQ

It is possible to check if an IRQ is ending by polling the control
register. This function must used with care: if an IRQ fires while the
host reads control register, the IRQ can be lost. However, it could be
useful in some cases.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200505123757.39506-8-Jerome.Pouiller@silabs.com


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