sfc: introduce ethernet pedit set action infrastructure

Introduce the initial ethernet pedit set action infrastructure in
preparation for adding mac src and dst pedit action offloads.

Co-developed-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>