forked from Mirrors/opensbi

As per the DT schema rules, the prefix should be vendor. As the PMU properties are generic for all vendors, change the prefix to riscv instead of pmu. Reviewed-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> Signed-off-by: Atish Patra <atish.patra@wdc.com>