bpf, docs: Add loongarch64 as arch supporting BPF JIT

As BPF JIT support for loongarch64 was added about one year ago
with commit 5dc61552

 ("LoongArch: Add BPF JIT support"), it
is appropriate to add loongarch64 as arch supporting BPF JIT in
bpf and sysctl docs as well.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/1695111937-19697-1-git-send-email-yangtiezhu@loongson.cn
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>