net: micrel: Add PHC support for lan8841

Add support for PHC and timestamping operations for the lan8841 PHY.
PTP 1-step and 2-step modes are supported, over Ethernet and UDP both
ipv4 and ipv6.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>