lib: Add early cpio decoder

Add a simple cpio decoder without library dependencies for the purpose
of extracting components from the initramfs blob for early kernel
uses.  Intended consumers so far are microcode and ACPI override.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1349043837-22659-2-git-send-email-trenn@suse.de
Cc: Len Brown <lenb@kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

Conflicts:
	lib/Makefile
earlycpio.c: Fix the confusing comment of find_cpio_data().

The comments of find_cpio_data() says:

  * @offset: When a matching file is found, this is the offset to the
  *          beginning of the cpio. ......

But according to the code,

  dptr = PTR_ALIGN(p + ch[C_NAMESIZE], 4);
  nptr = PTR_ALIGN(dptr + ch[C_FILESIZE], 4);
  ....
  *offset = (long)nptr - (long)data;	/* data is the cpio file */

@offset is the offset of the next file, not the matching file itself.
This is confused and may cause unnecessary waste of time to debug.
So fix it.

As Tejun Heo suggested, rename @offset to @nextoff which is more clear
to users. And also adjust the new comments.

Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Conflicts:
	lib/earlycpio.c