dt-bindings: watchdog: npcm: Add nuvoton,wpcm450-wdt

Add a compatible string for the WPCM450 SoC, which has the same watchdog
timer.

Signed-off-by: Jonathan Neuschäfer <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Reviewed-by: Joel Stanley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Joel Stanley <[e-mail]>

Documentation/devicetree/bindings/watchdog/nuvoton,npcm-wdt.txt

···
 expiry.
 
 Required properties:
-- compatible      : "nuvoton,npcm750-wdt" for NPCM750 (Poleg).
+- compatible      : "nuvoton,npcm750-wdt" for NPCM750 (Poleg), or
+                    "nuvoton,wpcm450-wdt" for WPCM450 (Hermon).
 - reg             : Offset and length of the register set for the device.
 - interrupts      : Contain the timer interrupt with flags for
                     falling edge.