mlxsw: spectrum: Prepare for multiple FW versions for Spectrum and Spectrum-2

Prepare for Spectrum-2 FW version checking and
make mlxsw_sp_fw_rev_validate() per-ASIC as well as required FW revision
and FW filename.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>