net: ti: icssg-prueth: add packet timestamping and ptp support

Add packet timestamping TS and PTP PHC clock support.

For AM65x and AM64x:
 - IEP1 is not used
 - IEP0 is configured in shadow mode with 1ms cycle and shared between
Linux and FW. It provides time and TS in number cycles, so special
conversation in ns is required.
 - IEP0 shared between PRUeth ports.
 - IEP0 supports PPS, periodic output.
 - IEP0 settime() and enabling PPS required FW interraction.
 - RX TS provided with each packet in CPPI5 descriptor.
 - TX TS returned through separate ICSSG hw queues for each port. TX TS
readiness is signaled by INTC IRQ. Only one packet at time can be requested
for TX TS.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Co-developed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>