dt-bindings: update riscv plic compatible string

Add the compatible string "thead,c900-plic" to the riscv plic
bindings to support allwinner d1 SOC which contains c906 core.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Anup Patel <anup@brainfault.org>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Samuel Holland <samuel@sholland.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220130135634.1213301-2-guoren@kernel.org

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

@@ -35,6 +35,10 @@ description:
   contains a specific memory layout, which is documented in chapter 8 of the
   SiFive U5 Coreplex Series Manual <https://static.dev.sifive.com/U54-MC-RVCoreIP.pdf>.
 
+  The thead,c900-plic is different from sifive,plic-1.0.0 in opensbi, the
+  T-HEAD PLIC implementation requires setting a delegation bit to allow access
+  from S-mode. So add thead,c900-plic to distinguish them.
+
 maintainers:
   - Sagar Kadam <sagar.kadam@sifive.com>
   - Paul Walmsley  <paul.walmsley@sifive.com>
@@ -42,12 +46,17 @@ maintainers:
 
 properties:
   compatible:
-    items:
-      - enum:
-          - sifive,fu540-c000-plic
-          - starfive,jh7100-plic
-          - canaan,k210-plic
-      - const: sifive,plic-1.0.0
+    oneOf:
+      - items:
+          - enum:
+              - sifive,fu540-c000-plic
+              - starfive,jh7100-plic
+              - canaan,k210-plic
+          - const: sifive,plic-1.0.0
+      - items:
+          - enum:
+              - allwinner,sun20i-d1-plic
+          - const: thead,c900-plic
 
   reg:
     maxItems: 1