Mellanox: Add new mlxsw_spectrum2 firmware 29.2000.2308

This is the first firmware file for the Spectrum-2 switch ASIC.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>

WHENCE

@@ -4546,6 +4546,7 @@ File: mellanox/mlxsw_spectrum-13.1910.622.mfa2
 File: mellanox/mlxsw_spectrum-13.2000.1122.mfa2
 File: mellanox/mlxsw_spectrum-13.2000.1886.mfa2
 File: mellanox/mlxsw_spectrum-13.2000.2308.mfa2
+File: mellanox/mlxsw_spectrum2-29.2000.2308.mfa2
 
 Licence:
  Copyright (c) 2017-2019 Mellanox Technologies, Ltd. All rights reserved.