forked from Mirrors/opensbi

As per the PLIC specification, maximum priority threshold value is 0x7. Even though, writing a higher value doesn't cause any error in qemu hifive unleashed, there may be some implementation which checks the upper and may result in an illegal access. Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> Reviewed-by: Anup Patel <anup.patel@wdc.com>