forked from Mirrors/opensbi

According to the description in "riscv-state-enable[0]", to access
h/scontext in S-Mode, we need to enable the 57th bit.
If it is not enabled, an "illegal instruction" error will occur.
Link: a28bfae443/content.adoc
[0]
Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
Reviewed-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>