ice: PTP: Clean up timestamp registers correctly

E822 PHY TS registers should not be written and the only way to clean up
them is to reset QUAD memory.

To ensure that the status bit for the timestamp index is cleared, ensure
that ice_clear_phy_tstamp implementations first read the timestamp out.
Implementations which can write the register continue to do so.

Add a note to indicate this function should only be called on timestamps
which have their valid bit set. Update the dynamic debug messages to
reflect the actual action taken.

Signed-off-by: Karol Kolacinski <karol.kolacinski@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>