kbuild: extract modules.builtin.modinfo from vmlinux.unstripped

kbuild: extract modules.builtin.modinfo from vmlinux.unstripped

Currently, we assume all the data for modules.builtin.modinfo are
available in vmlinux.o.

This makes it impossible for modpost, which is invoked after vmlinux.o,
to add additional module info.

This commit moves the modules.builtin.modinfo rule after modpost.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Link: https://patch.msgid.link/cdb3e5b9a739666b755cd0097dc34ab69c350e51.1758182101.git.legion@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>