kbuild: keep .modinfo section in vmlinux.unstripped

Keep the .modinfo section during linking, but strip it from the final
vmlinux.

Adjust scripts/mksysmap to exclude modinfo symbols from kallsyms.

This change will allow the next commit to extract the .modinfo section
from the vmlinux.unstripped intermediate.

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/aaf67c07447215463300fccaa758904bac42f992.1758182101.git.legion@kernel.org


Signed-off-by: Nathan Chancellor <nathan@kernel.org>