forked from Mirrors/opensbi

Over the years, no uses of sbi_trap_exit() have been found so remove it and also remove related code from fw_base.S and sbi_scratch.h. Signed-off-by: Anup Patel <apatel@ventanamicro.com> Reviewed-by: Samuel Holland <samuel.holland@sifive.com> Tested-by: Samuel Holland <samuel.holland@sifive.com>