bpf, arm64: Support unconditional bswap

Add JIT support for unconditional bswap instructions.

Signed-off-by: Xu Kuohai <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Tested-by: Florent Revest <[email protected]>
Acked-by: Florent Revest <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]