spi: add spi-loopback-test to build framework

adding the spi-loopback-test module to Kconfig and Makefile

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 8b9c2a3..0876d59 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -689,6 +689,15 @@
 	  Note that this application programming interface is EXPERIMENTAL
 	  and hence SUBJECT TO CHANGE WITHOUT NOTICE while it stabilizes.
 
+config SPI_LOOPBACK_TEST
+	tristate "spi loopback test framework support"
+	depends on m
+	help
+	  This enables the SPI loopback testing framework driver
+
+	  primarily used for development of spi_master drivers
+	  and to detect regressions
+
 config SPI_TLE62X0
 	tristate "Infineon TLE62X0 (for power switching)"
 	depends on SYSFS