dt-bindings: arm: Document Phytium FTC series cpu

Document the compatible string for the FTC series cpus found in Phytium
SoCs.

Signed-off-by: Chen Baozi <chenbaozi@phytium.com.cn>
Signed-off-by: Wang Yinfeng <wangyinfeng@phytium.com.cn>
Signed-off-by: Jiakun Shuai <shuaijiakun1288@phytium.com.cn>

Documentation/devicetree/bindings/arm/cpus.yaml

@@ -182,6 +182,12 @@ properties:
       - nvidia,tegra132-denver
       - nvidia,tegra186-denver
       - nvidia,tegra194-carmel
+      - phytium,ftc310
+      - phytium,ftc660
+      - phytium,ftc661
+      - phytium,ftc662
+      - phytium,ftc663
+      - phytium,ftc664
       - qcom,krait
       - qcom,kryo
       - qcom,kryo240