ARM: configs: at91: sama5: add support for KSZ ethernet switches

Enable DSA and KSZ9477 support as modules. Ethernet switches are used by
the SAMA5D2-ICP board.

Signed-off-by: Razvan Stefanescu <razvan.stefanescu@microchip.com>
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200723162434.1983643-1-codrin.ciubotariu@microchip.com