bpf, arm64: Support sign-extension mov instructions

Add JIT support for BPF sign-extension mov instructions with arm64
SXTB/SXTH/SXTW instructions.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Florent Revest <revest@chromium.org>
Acked-by: Florent Revest <revest@chromium.org>
Link: https://lore.kernel.org/bpf/20230815154158.717901-4-xukuohai@huaweicloud.com