Add tests/Makefile targets for moved test helpers

Everything that has been moved to tests/src needs a Makefile target in
order to be built.

Signed-off-by: David Horstmann <david.horstmann@arm.com>

tests/Makefile

diff --git a/tests/Makefile b/tests/Makefile
index c6d8e2c..4824632 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -185,12 +185,17 @@
 endif
 TEST_OBJS_DEPS += src/test_certs.h src/test_keys.h
 
-# Rule to compile common test C files in src folder
-src/%.o : src/%.c $(TEST_OBJS_DEPS)
+# Rule to compile common test C files in framework
+../framework/tests/src/%.o : ../framework/tests/src/%.c $(TEST_OBJS_DEPS)
 	echo "  CC    $<"
 	$(CC) $(LOCAL_CFLAGS) $(CFLAGS) -o $@ -c $<
 
-src/drivers/%.o : src/drivers/%.c
+../framework/tests/src/drivers/%.o : ../framework/tests/src/drivers/%.c
+	echo "  CC    $<"
+	$(CC) $(LOCAL_CFLAGS) $(CFLAGS) -o $@ -c $<
+
+# Rule to compile common test C files in src folder
+src/%.o : src/%.c $(TEST_OBJS_DEPS)
 	echo "  CC    $<"
 	$(CC) $(LOCAL_CFLAGS) $(CFLAGS) -o $@ -c $<