initramfs: add support for in-kernel initramfs compressed with LZO

Add the necessary parts to be enable the use of LZO-compressed initramfs
build into the kernel.

Signed-off-by: Albin Tonnerre <albin.tonnerre@free-electrons.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>