mlxsw: reg: Add Monitoring FW General Debug Register

Introduce MFGD register that is used to configure firmware debugging.

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