modprobe: show builtin label on --show-depends

modprobe: show builtin label on --show-depends

Previously, we didn't handle builtins very well, displaying things like:

$ modprobe -D btrfs
insmod /lib/modules/3.2.6-foo/kernel/crypto/crc32c.ko.gz
insmod (null)
insmod /lib/modules/3.2.6-foo/kernel/lib/libcrc32c.ko.gz
insmod /lib/modules/3.2.6-foo/kernel/lib/zlib_deflate/zlib_deflate.ko.gz
insmod /lib/modules/3.2.6-foo/kernel/fs/btrfs/btrfs.ko.gz

Follow module-init-tools and show builtins with the label 'builtin' and
their name:

$ modprobe -D btrfs
insmod /lib/modules/3.2.6-foo/kernel/crypto/crc32c.ko.gz
builtin intel_crc32c
insmod /lib/modules/3.2.6-foo/kernel/lib/libcrc32c.ko.gz
insmod /lib/modules/3.2.6-foo/kernel/lib/zlib_deflate/zlib_deflate.ko.gz
insmod /lib/modules/3.2.6-foo/kernel/fs/btrfs/btrfs.ko.gz