dt-bindings: riscv: add a capacity-dmips-mhz cpu property

Since commit 03f11f03 ("RISC-V: Parse cpu topology during boot.")
RISC-V has used the generic arch topology code, which provides for
disparate CPU capacities. We never defined a binding to acquire this
information from the DT though, so document the one already used by the
generic arch topology code: "capacity-dmips-mhz".

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230104180513.1379453-3-conor@kernel.org


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>