drivers: net: add NXP ENETC ethernet driver

Adds a driver for NXP ENETC ethernet controller currently integrated in
LS1028A.  ENETC is a fairly straight-forward BD ring device and interfaces
are presented as PCI EPs on the SoC ECAM.

Signed-off-by: Catalin Horghidan <catalin.horghidan@nxp.com>
Signed-off-by: Alex Marginean <alexm.osslist@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>