sched_ext: Fix the incorrect bpf_list kfunc API in common.bpf.h.

Now BPF only supports bpf_list_push_{front,back}_impl kfunc, not bpf_list_
push_{front,back}.

This patch fix this issue. Without this patch, if we use bpf_list kfunc
in scx, the BPF verifier would complain:

libbpf: extern (func ksym) 'bpf_list_push_back': not found in kernel or
module BTFs
libbpf: failed to load object 'scx_foo'
libbpf: failed to load BPF skeleton 'scx_foo': -EINVAL

With this patch, the bpf list kfunc will work as expected.

Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
Fixes: 2a52ca7c ("sched_ext: Add scx_simple and scx_example_qmap example schedulers")
Signed-off-by: Tejun Heo <tj@kernel.org>