Previous commits installed non-elf files into /lib/modules/$VER/.
COLLECT_KERNEL_DEBUG tries to strip all files and these two files
break the build.
Fix it by copying only kernel modules for debug info collection.
Fixes: e1d8e57614 ("kernel: include modinfo for built-in modules")
Fixes: 29f6da4340 ("kernel: include built-in module list")
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>