x86_64: Add convenience target to run the test suite

Once infix has been built, the test suite can now be run by issuing:

    make infix-check

board/x86_64/board.mk

@@ -0,0 +1,8 @@
+test-dir = $(BR2_EXTERNAL_INFIX_PATH)/test
+
+.PHONY: infix-check
+infix-check:
+	$(test-dir)/env \
+		-q $(test-dir)/virt/dual \
+		-f $(BINARIES_DIR)/infix-x86_64.img \
+		$(BR2_EXTERNAL_INFIX_PATH)/9pm/9pm.py $(test-dir)/case/all.yaml