Add proper compatible for Platform-Level Interrupt Controller to silence
dtbs_check warnings:
  interrupt-controller@
c000000: compatible: ['sifive,plic-1.0.0'] is too short
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Tested-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Link: https://lore.kernel.org/r/20210920130412.145231-2-krzysztof.kozlowski@canonical.com
 
                ranges;
                plic0: interrupt-controller@c000000 {
                        #interrupt-cells = <1>;
-                       compatible = "sifive,plic-1.0.0";
+                       compatible = "sifive,fu540-c000-plic", "sifive,plic-1.0.0";
                        reg = <0x0 0xc000000 0x0 0x4000000>;
                        riscv,ndev = <53>;
                        interrupt-controller;