bpf, x64: fix stack layout of JITed bpf code

[ Upstream commit fe8d9571dc50232b569242fac7ea6332a654f186 ]

Since commit 177366bf the %rbp stopped pointing to %rbp of the
previous stack frame. That broke frame pointer based stack unwinding.
This commit is a partial revert of it.
Note that the location of tail_call_cnt is fixed, since the verifier
enforces MAX_BPF_STACK stack size for programs with tail calls.

Fixes: 177366bf ("bpf: change x86 JITed program stack layout")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>