[spi][swspi-srv] Enable SW SPI loopback by default

Bug: 132281443
Bug: 176433178
Change-Id: Ifc39d28f1e78b77eba7ebd2f3857ce3715b30c7d
diff --git a/spi/swspi-srv/rules.mk b/spi/swspi-srv/rules.mk
index 60569b3..b5cc3c4 100644
--- a/spi/swspi-srv/rules.mk
+++ b/spi/swspi-srv/rules.mk
@@ -28,6 +28,9 @@
     trusty/user/base/lib/spi/srv \
     trusty/user/base/lib/tipc \
 
+# Include software implementation of SPI loopback device by default
+WITH_SW_SPI_LOOPBACK ?= true
+
 ifeq (true,$(call TOBOOL,$(WITH_SW_SPI_LOOPBACK)))
     MODULE_DEFINES += WITH_SW_SPI_LOOPBACK=1
 endif