mlxsw: reg: Add Management General Peripheral Information Register

Add MGPIR - Management General Peripheral Information Register, which
allows software to query the hardware and firmware general information
of peripheral entities as Gearboxes etc.

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