dt-bindings: arm: cpus: Add Cortex A520, A720, and X4

Add compatible strings for the Arm Cortex-A520, Cortex-A720, and
Cortex-X4 2023 CPUs.

Acked-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/arm/cpus.yaml

···
       - arm,cortex-a78ae
       - arm,cortex-a78c
       - arm,cortex-a510
+      - arm,cortex-a520
       - arm,cortex-a710
       - arm,cortex-a715
+      - arm,cortex-a720
       - arm,cortex-m0
       - arm,cortex-m0+
       - arm,cortex-m1
···
       - arm,cortex-x1c
       - arm,cortex-x2
       - arm,cortex-x3
+      - arm,cortex-x4
       - arm,neoverse-e1
       - arm,neoverse-n1
       - arm,neoverse-n2