bpf, arm64: Enable the inline of bpf_kptr_xchg()

ARM64 bpf jit satisfies the following two conditions:
1) support BPF_XCHG() on pointer-sized word.
2) the implementation of xchg is the same as atomic_xchg() on
   pointer-sized words. Both of these two functions use arch_xchg() to
   implement the exchange.

So enable the inline of bpf_kptr_xchg() for arm64 bpf jit.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20240119102529.99581-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>