staging: wfx: use threaded IRQ with SPI

Currently, the SPI implementation use a workqueue to acknowledge IRQ
while the SDIO-OOB implementation use a threaded IRQ.

The threaded also offers the advantage to allow level triggered IRQs.

Uniformize the code and use threaded IRQ in both case. Therefore, prefer
level triggered IRQs if the user does not specify it in the DT.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200505123757.39506-7-Jerome.Pouiller@silabs.com


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