ARM: at91: Documentation: add lan966 family

Add the new LAN966 ARMv7 based SoC family from Microchip.

Signed-off-by: Kavyasree Kotagiri <kavyasree.kotagiri@microchip.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
[nicolas.ferre@microchip.com: move entry as part of new Cortex-A7 core type]
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20211004105926.5696-3-kavyasree.kotagiri@microchip.com