NFC: nxp-nci: Make firmware GPIO pin optional

NFC: nxp-nci: Make firmware GPIO pin optional

There are other NXP NCI compatible NFC controllers such as the PN7150
that use an integrated firmware and therefore do not have a GPIO to
select firmware downloading mode. To support this kind of controller,
let's make the firmware GPIO optional.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20201201113921.6572-1-frieder.schrempf@kontron.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>