bpf, arm64: Replace STACK_ALIGN() with round_up() to align stack size

Use the common function round_up() directly to show the align size
explicitly, the function STACK_ALIGN() is needless, remove it. Other
JITs also just rely on round_up().

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/1620651119-5663-1-git-send-email-yangtiezhu@loongson.cn