ANDROID: inject correct HMAC digest into fips140.ko at build time

Inject the HMAC digest into the fips140.ko module once it has been
built. This involves a post-link step, so we need to use a special
Makefile that is wired up in the right way, and includes the special
handling only for fips140.ko in particular.

Bug: 153614920
Bug: 188620248
Change-Id: Ic66086a05fa997850ca15dedbbc14fc73f6f0da6
Signed-off-by: Ard Biesheuvel <ardb@google.com>