dt-bindings: watchdog: sama5d4_wdt: add microchip,sam9x60-wdt compatible

The Atmel sama5d4_wdt needs to be compatible with microchip,sam9x60-wdt
The sama5d4_wdt driver is updated to work with both hardware blocks
(sama5d4/sama5d2 and sam9x60 based blocks)
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1573806579-7981-2-git-send-email-eugen.hristev@microchip.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/atmel-sama5d4-wdt.txt

 * Atmel SAMA5D4 Watchdog Timer (WDT) Controller
 
 Required properties:
-- compatible: "atmel,sama5d4-wdt"
+- compatible: "atmel,sama5d4-wdt" or "microchip,sam9x60-wdt"
 - reg: base physical address and length of memory mapped region.
 
 Optional properties: