forked from Mirrors/opensbi

All string functions are part of libsbi. It makes more sense to rename them to sbi_string.x as the libsbi can be linked with external libraries that can have similar implementation. Signed-off-by: Atish Patra <atish.patra@wdc.com> Acked-by: Anup Patel <anup.patel@wdc.com>