dt-bindings: riscv: explicitly mention assumption of Zicntr & Zihpm support

Similar to commit 41ebfc9 ("dt-bindings: riscv: explicitly mention
assumption of Zicsr & Zifencei support"), the Zicntr and Zihpm
extensions also used to be part of the base ISA but were removed after
the bindings were merged. Document the assumption of their presence in
the base ISA.

Suggested-by: Palmer Dabbelt <[email protected]>
Signed-off-by: Conor Dooley <[email protected]>
Acked-by: Rob Herring <[email protected]>
Link: https://lore.kernel.org/r/20230607-rerun-retinal-5e8ba89e98f1@spud
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: ConchuOD

Documentation/devicetree/bindings/riscv/cpus.yaml

@@ -89,8 +89,8 @@ properties:
       Due to revisions of the ISA specification, some deviations
       have arisen over time.
       Notably, riscv,isa was defined prior to the creation of the
-      Zicsr and Zifencei extensions and thus "i" implies
-      "zicsr_zifencei".
+      Zicntr, Zicsr, Zifencei and Zihpm extensions and thus "i"
+      implies "zicntr_zicsr_zifencei_zihpm".
 
       While the isa strings in ISA specification are case
       insensitive, letters in the riscv,isa string must be all