kbuild runs "find" on each entry in CONFIG_INITRAMFS_SOURCE that is a
directory. The order of the file listing output by "find" matter for
build reproducability, hence this patch applies "sort" to get
deterministic results.

Without this patch, two different machines with identical initramfs
directory input may produce differing initramfs cpio archives (different
hash) due to the different order of the files within the archive.
Signed-off-by: Bjørn Forsman <bjorn.forsman@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>