mlxsw: Extend MRSR pack() function to support new commands

Currently mlxsw_reg_mrsr_pack() always sets 'command=1'. As preparation for
support of new reset flow, pass the command as an argument to the
function and add an enum for this field.

For now, always pass 'command=1' to the pack() function.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>