mlxsw: spectrum_ptp: Use 'struct mlxsw_sp_ptp_clock' per ASIC

Currently, there is one shared structure that holds the required
structures for PTP clock. Most of the existing fields are relevant only
for Spectrum-1 (cycles, timecounter, and more). Rename the structure to
be specific for Spectrum-1 and align the existing code. Add a common
structure which includes the structures which will be used also for
Spectrum-2. This structure will be returned from clock_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>