Remove direct usage of __attribute__((foo))

Migrate all direct usage of __attribute__ to usage of their
corresponding macros from cdefs.h.
e.g.:
 - __attribute__((unused)) -> __unused

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
diff --git a/include/drivers/auth/img_parser_mod.h b/include/drivers/auth/img_parser_mod.h
index d80e0fb..79d7d79 100644
--- a/include/drivers/auth/img_parser_mod.h
+++ b/include/drivers/auth/img_parser_mod.h
@@ -77,7 +77,7 @@
 /* Macro to register an image parser library */
 #define REGISTER_IMG_PARSER_LIB(_type, _name, _init, _check_int, _get_param) \
 	static const img_parser_lib_desc_t __img_parser_lib_desc_##_type \
-	__attribute__ ((section(".img_parser_lib_descs"), used)) = { \
+	__section(".img_parser_lib_descs") __used = { \
 		.img_type = _type, \
 		.name = _name, \
 		.init = _init, \