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: 5f9ae91 ("kbuild: Build kernel module BTFs if BTF is enabled and pahole supports it")
Reported-by: Vincent Li <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Link: https://lore.kernel.org/bpf/CAK3+h2xiFfzQ9UXf56nrRRP=p1+iUxGoEP5B+aq9MDT5jLXDSg@mail.gmail.com [0]
Link: https://lore.kernel.org/bpf/[email protected]

Author: anakryiko

lib/Kconfig.debug

@@ -375,7 +375,7 @@ config DEBUG_INFO_SPLIT
 	  Incompatible with older versions of ccache.
 
 config DEBUG_INFO_BTF
-	bool "Generate BTF typeinfo"
+	bool "Generate BTF type information"
 	depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
 	depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
 	depends on BPF_SYSCALL
@@ -408,7 +408,8 @@ config PAHOLE_HAS_LANG_EXCLUDE
 	  using DEBUG_INFO_BTF_MODULES.
 
 config DEBUG_INFO_BTF_MODULES
-	def_bool y
+	bool "Generate BTF type information for kernel modules"
+	default y
 	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
 	help
 	  Generate compact split BTF type information for kernel modules.