net: cortina_ni: Add eth support for Cortina Access CAxxxx SoCs

Add Cortina Access Ethernet device driver for CAxxxx SoCs.
This driver supports both legacy and DM_ETH network models.

Signed-off-by: Aaron Tseng <aaron.tseng@cortina-access.com>
Signed-off-by: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>
Signed-off-by: Abbie Chang <abbie.chang@cortina-access.com>

CC: Joe Hershberger <joe.hershberger@ni.com>
CC: Abbie Chang <abbie.chang@Cortina-Access.com>
CC: Tom Rini <trini@konsulko.com>