dt-bindings: atmel-sysreg: add "microchip, sama7g5-chipid"

Add DT binding for SAMA7G5's CHIPID.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/1611318097-8970-7-git-send-email-claudiu.beznea@microchip.com