In commit bc8713e7af the SPI functionality was made available
conditionally depending on the FPGA version number. For this,
all SPI entries were removed from the X4XX_GPIO_SRC_RADIO variable
and put into an own variable. But therefore SPI was not available
anymore as valid source for GPIO. This change reintroduces SPI and
thus enables the SPI functionality again.
Co-authored-by: Javier Valenzuela <javier.valenzuela@ni.com>