qed: Acquire/release ptt_ptp lock when enabling/disabling PTP.

Move the code for acquiring/releasing ptt_ptp lock to ptp specific
implementations i.e., ptp_enable()/disable() respectively.

Signed-off-by: Sudarsana Reddy Kalluru <Sudarsana.Kalluru@cavium.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>