dts: riscv: include riscv,cpus.yaml in qingke-v2

This commit updates the qingke-v2 binding to include `riscv,cpus.yaml`
instead of `cpu.yaml`.

Signed-off-by: Jianxiong Gu <jianxiong.gu@outlook.com>

dts/bindings/cpu/wch,qingke-v2.yaml

@@ -5,4 +5,4 @@ description: WCH QingKe V2 RISC-V MCU
 
 compatible: "wch,qingke-v2"
 
-include: cpu.yaml
+include: riscv,cpus.yaml

dts/riscv/wch/qingke-v2.dtsi

@@ -16,6 +16,7 @@
 			device_type = "cpu";
 			compatible = "wch,qingke-v2";
 			reg = <0>;
+			riscv,isa = "rv32ec_zicsr_zifencei";
 		};
 	};