dt-bindings: interrupt-controller: add SpacemiT K3 IMSIC

Add compatible string for SpacemiT K3 IMSIC.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Guodong Xu <guodong@riscstar.com>
Link: https://lore.kernel.org/r/20260115-k3-basic-dt-v5-4-6990ac9f4308@riscstar.com
Signed-off-by: Yixun Lan <dlan@kernel.org>

Author: docularxu

Documentation/devicetree/bindings/interrupt-controller/riscv,imsics.yaml

@@ -48,6 +48,7 @@ properties:
     items:
       - enum:
           - qemu,imsics
+          - spacemit,k3-imsics
       - const: riscv,imsics
 
   reg: