forked from Mirrors/opensbi

As per the RISC-V privilege specification, WFI can be implemented as a NOP. Software should ensure that relevant interrupt pending bits are set. Otherwise, loop back to WFI. Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>