mlxsw: spectrum_ptp: Use 'struct mlxsw_sp_ptp_state' per ASIC

Currently, there is one shared structure that holds the required
structures and details for PTP. Most of the existing fields are relevant
only for Spectrum-1 (hash table, lock for hash table, delayed work, and
more). Rename the structure to be specific for Spectrum-1 and align the
existing code. Add a common structure which includes
'struct mlxsw_sp *mlxsw_sp' and will be returned from ptp_init()
operation, as the definition is shared between all ASICs' operations.

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: David S. Miller <davem@davemloft.net>