dt-bindings: interrupt-controller: sifive,plic: Add pic64gx compatibility

As mention in sifive,plic-1.0.0.yaml, a specific compatible should be used
for pic64gx, so here it is.

Signed-off-by: Pierre-Henry Moussay <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Signed-off-by: Conor Dooley <[e-mail]>
Link: https://patch.msgid.link/20251117-evict-corridor-5efe40101eea@spud
Signed-off-by: Rob Herring (Arm) <[e-mail]>

Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml

···
           - enum:
               - canaan,k210-plic
               - eswin,eic7700-plic
+              - microchip,pic64gx-plic
               - sifive,fu540-c000-plic
               - spacemit,k1-plic
               - starfive,jh7100-plic