iavf: add initial framework for registering PTP clock

Add the iavf_ptp.c file and fill it in with a skeleton framework to
allow registering the PTP clock device.
Add implementation of helper functions to check if a PTP capability
is supported and handle change in PTP capabilities.
Enabling virtual clock would be possible, though it would probably
perform poorly due to the lack of direct time access.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Sai Krishna <saikrishnag@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Co-developed-by: Ahmed Zaki <ahmed.zaki@intel.com>
Signed-off-by: Ahmed Zaki <ahmed.zaki@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Co-developed-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>