mxssb: Add full list of possible command tags

Fill in the full table of SB command tags as they are listed in the
SB image specification.
Signed-off-by: Marek Vasut <marex@denx.de>

mxssb.h

@@ -134,9 +134,15 @@ struct sb_command {
 	};
 };
 
-#define ROM_TAG_CMD		0x1
-#define ROM_LOAD_CMD		0x2
-#define ROM_CALL_CMD		0x5
+enum sb_tag {
+	ROM_NOP_CMD	= 0x00,
+	ROM_TAG_CMD	= 0x01,
+	ROM_LOAD_CMD	= 0x02,
+	ROM_FILL_CMD	= 0x03,
+	ROM_JUMP_CMD	= 0x04,
+	ROM_CALL_CMD	= 0x05,
+	ROM_MODE_CMD	= 0x06
+};
 
 struct sb_source_entry {
 	uint8_t		tag;