spi: Allow compile test of bcm2835aux if !GPIOLIB

The GPIO subsystem provides dummy GPIO consumer functions if GPIOLIB is
not enabled. Hence drivers that depend on GPIOLIB, but use GPIO consumer
functionality only, can still be compiled if GPIOLIB is not enabled.

Relax the dependency of SPI_BCM2835AUX on GPIOLIB if COMPILE_TEST is
enabled.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Mark Brown <broonie@kernel.org>