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

Documentation/devicetree/bindings/arm/atmel-sysregs.txt

 Atmel system registers
 
 Chipid required properties:
-- compatible: Should be "atmel,sama5d2-chipid"
+- compatible: Should be "atmel,sama5d2-chipid" or "microchip,sama7g5-chipid"
 - reg : Should contain registers location and length
 
 PIT Timer required properties: