forked from Mirrors/opensbi

This patch adds initial implementation of sbi_exit() API which can be used to perform OpenSBI exit sequence for current HART. The sbi_exit() implementation will be further extended by subsequent patches. Signed-off-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Atish Patra <atish.patra@wdc.com>