spi: xtensa-xtfpga: Enable driver compilation with COMPILE_TEST

This helps increasing build testing coverage.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/Kconfig

@@ -522,7 +522,7 @@ config SPI_XILINX
 
 config SPI_XTENSA_XTFPGA
 	tristate "Xtensa SPI controller for xtfpga"
-	depends on XTENSA && XTENSA_PLATFORM_XTFPGA
+	depends on (XTENSA && XTENSA_PLATFORM_XTFPGA) || COMPILE_TEST
 	select SPI_BITBANG
 	help
 	  SPI driver for xtfpga SPI master controller.