greybus: define greybus wide protocol request numbers

Some request numbers (like invalid and get_version) are same across all
protocols. Create common macros for them.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/greybus_protocols.h

@@ -99,6 +99,10 @@ struct gb_operation_msg_hdr {
 };
 
 
+/* Generic request numbers supported by all modules */
+#define GB_REQUEST_TYPE_INVALID			0x00
+#define GB_REQUEST_TYPE_PROTOCOL_VERSION	0x01
+
 /* Control Protocol */
 
 /* version request has no payload */