UPSTREAM: kbuild: Consolidate header generation from ASM offset information

Largely redundant code is used in different places to generate C headers
from offset information extracted from assembly language output.
Consolidate the code in Makefile.lib and use this instead.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
(cherry picked from commit ebf003f0)
Signed-off-by: Greg Hackmann <ghackmann@google.com>

Change-Id: I0acd54dd27c0cf0868f221bd63728a9b67320b25