ptp: add ToD device driver for Intel FPGA cards

ptp: add ToD device driver for Intel FPGA cards

Adding a DFL (Device Feature List) device driver of ToD device for
Intel FPGA cards.

The Intel FPGA Time of Day(ToD) IP within the FPGA DFL bus is exposed
as PTP Hardware clock(PHC) device to the Linux PTP stack to synchronize
the system clock to its ToD information using phc2sys utility of the
Linux PTP stack. The DFL is a hardware List within FPGA, which defines
a linked list of feature headers within the device MMIO space to provide
an extensible way of adding subdevice features.

Signed-off-by: Raghavendra Khadatare <raghavendrax.anand.khadatare@intel.com>
Signed-off-by: Tianfei Zhang <tianfei.zhang@intel.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230328142455.481146-1-tianfei.zhang@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>