virtchnl: add PTP virtchnl definitions

PTP capabilities are negotiated using virtchnl commands. There are two
available modes of the PTP support: direct and mailbox. When the direct
access to PTP resources is negotiated, virtchnl messages returns a set
of registers that allow read/write directly. When the mailbox access to
PTP resources is negotiated, virtchnl messages are used to access
PTP clock and to read the timestamp values.

Virtchnl API covers both modes and exposes a set of PTP capabilities.

Using virtchnl API, the driver recognizes also HW abilities - maximum
adjustment of the clock and the basic increment value.

Additionally, API allows to configure the secondary mailbox, dedicated
exclusively for PTP purposes.

Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Milena Olech <milena.olech@intel.com>
Tested-by: Mina Almasry <almasrymina@google.com>
Tested-by: Samuel Salin <Samuel.salin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>