forked from Mirrors/opensbi

We should check and access N-extension CSRs in sbi_hart_switch_mode() when next_mode is u-mode because N-extension is optional. Signed-off-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Alistair Francis <alistair.francis@wdc.com> Reviewed-by: Atish Patra <atish.patra@wdc.com>