efi_loader: add helper macro to construct protocol objects

There are a bunch of protocols which should be exposed by GUID but are
not.  Add a helper macro to create an efi_object, to avoid much typing.

Note that using the pointer for efiobj->handle is semi-arbitrary.  We
just need a unique value to match the efiobj supporting the protocol
with the handle that LocateHandle() returns..

See LibLocateProtocol() in gnu-efi.  It does LocateHandle() to find all
the handles, and then loops over them calling HandleProtocol() with the
GUID of the protocol it is trying to find.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

include/efi_loader.h

@@ -66,6 +66,14 @@ struct efi_object {
 	void *handle;
 };
 
+#define EFI_PROTOCOL_OBJECT(_guid, _protocol) (struct efi_object){	\
+	.protocols = {{							\
+		.guid = &(_guid),	 				\
+		.protocol_interface = (void *)(_protocol), 		\
+	}},								\
+	.handle = (void *)(_protocol),					\
+}
+
 /**
  * struct efi_event
  *