common/iavf: support Rx timestamp in virtual channel

common/iavf: support Rx timestamp in virtual channel

Add new ops and structures to support VF to support Rx timestamp
on flex descriptor.

"VIRTCHNL_OP_1588_PTP_GET_CAPS" ops is sent by the VF to request PTP
capabilities and responded by the PF with capabilities enabled for
that VF.

"VIRTCHNL_OP_1588_PTP_GET_TIME" ops is sent by the VF to request
the current time of the PHC. The PF will respond by reading the
device time and reporting it back to the VF.

Signed-off-by: Simei Su <simei.su@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>