bnxt_en: Add PTP clock APIs, ioctls, and ethtool methods

Add the clock APIs to set/get/adjust the hw clock, and the related
ioctls and ethtool methods.

v2: Propagate error code from ptp_clock_register().
    Add spinlock to serialize access to the timecounter.  The
    timecounter is accessed in process context and the RX datapath.
    Read the PHC using direct registers.

Reviewed-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>