riscv: hw: Drop "clock-frequency" property of cpu nodes

riscv: hw: Drop "clock-frequency" property of cpu nodes

The "clock-frequency" property of cpu nodes isn't required. Drop it.

This is to keep in sync with Linux kernel commit below:
https://patchwork.kernel.org/patch/11133031/

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>