The bindings assumed that the gpios properties were always there, which
made the NO_TX and NO_RX mode not usable from device tree. Add extra
checks to make sure that the driver can work if either MOSI or MISO is
not used.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com> Cc: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>