ice: enable receive hardware timestamping

Add SIOCGHWTSTAMP and SIOCSHWTSTAMP ioctl handlers to respond to
requests to enable timestamping support. If the request is for enabling
Rx timestamps, set a bit in the Rx descriptors to indicate that receive
timestamps should be reported.

Hardware captures receive timestamps in the PHY which only captures part
of the timer, and reports only 40 bits into the Rx descriptor. The upper
32 bits represent the contents of GLTSYN_TIME_L at the point of packet
reception, while the lower 8 bits represent the upper 8 bits of
GLTSYN_TIME_0.

The networking and PTP stack expect 64 bit timestamps in nanoseconds. To
support this, implement some logic to extend the timestamps by using the
full PHC time.

If the Rx timestamp was captured prior to the PHC time, then the real
timestamp is

  PHC - (lower_32_bits(PHC) - timestamp)

If the Rx timestamp was captured after the PHC time, then the real
timestamp is

  PHC + (timestamp - lower_32_bits(PHC))

These calculations are correct as long as neither the PHC timestamp nor
the Rx timestamps are more than 2^32-1 nanseconds old. Further, we can
detect when the Rx timestamp is before or after the PHC as long as the
PHC timestamp is no more than 2^31-1 nanoseconds old.

In that case, we calculate the delta between the lower 32 bits of the
PHC and the Rx timestamp. If it's larger than 2^31-1 then the Rx
timestamp must have been captured in the past. If it's smaller, then the
Rx timestamp must have been captured after PHC time.

Add an ice_ptp_extend_32b_ts function that relies on a cached copy of
the PHC time and implements this algorithm to calculate the proper upper
32bits of the Rx timestamps.

Cache the PHC time periodically in all of the Rx rings. This enables
each Rx ring to simply call the extension function with a recent copy of
the PHC time. By ensuring that the PHC time is kept up to date
periodically, we ensure this algorithm doesn't use stale data and
produce incorrect results.

To cache the time, introduce a kworker and a kwork item to periodically
store the Rx time. It might seem like we should use the .do_aux_work
interface of the PTP clock. This doesn't work because all PFs must cache
this time, but only one PF owns the PTP clock device.

Thus, the ice driver will manage its own kthread instead of relying on
the PTP do_aux_work handler.

With this change, the driver can now report Rx timestamps on all
incoming packets.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>