cxgb4: Add PTP Hardware Clock (PHC) support

Add PTP IEEE-1588 support and make it accessible via PHC subsystem.
The functionality is enabled for T5/T6 adapters. Driver interfaces with
Firmware to program and adjust the clock offset.

Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Atul Gupta <atul.gupta@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>