bpf, kconfig: Fix DEBUG_INFO_BTF_MODULES Kconfig definition

Turns out that due to CONFIG_DEBUG_INFO_BTF_MODULES not having an
explicitly specified "menu item name" in Kconfig, it's basically
impossible to turn it off (see [0]).

This patch fixes the issue by defining menu name for
CONFIG_DEBUG_INFO_BTF_MODULES, which makes it actually adjustable
and independent of CONFIG_DEBUG_INFO_BTF, in the sense that one can
have DEBUG_INFO_BTF=y and DEBUG_INFO_BTF_MODULES=n.

We still keep it as defaulting to Y, of course.

Fixes: 5f9ae91f

 ("kbuild: Build kernel module BTFs if BTF is enabled and pahole supports it")
Reported-by: Vincent Li <vincent.mc.li@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/CAK3+h2xiFfzQ9UXf56nrRRP=p1+iUxGoEP5B+aq9MDT5jLXDSg@mail.gmail.com [0]
Link: https://lore.kernel.org/bpf/20240404220344.3879270-1-andrii@kernel.org