idpf: add padding to PTP virtchnl structures

Add padding to virtchnl2 PTP structures to match the Control Plane
expected message sizes:
* virtchnl2_ptp_get_dev_clk_time: 8 -> 16 bytes
* virtchnl2_ptp_set_dev_clk_time: 8 -> 16 bytes
* virtchnl2_ptp_get_cross_time: 16 -> 24 bytes

The FW expects the above sizes and PTP negotiation fails due to the
mismatch. Previously neither the FW nor the driver checked message/reply
sizes strictly, so the problem appeared only after recent validation
improvements.

reproduction steps:
ptp4l -i <pf> -m
Observe: failed to open /dev/ptp0: Permission denied

Fixes: bf27283ba594 ("virtchnl: add PTP virtchnl definitions")
Cc: stable@vger.kernel.org
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Przemyslaw Korba <przemyslaw.korba@intel.com>