inmates: Build library archive and link it implicitly

inmates: Build library archive and link it implicitly

Kbuild already comes with support for building lib.a archives from a set
of objects. Use this to build inmate libraries for x86, here in 64 and
32-bit form, and for ARM. Link against the correct libraries implicitly
so that the demos no longer have to state their dependencies explicitly.

This will also allow to use the inmate libraries from different folders
than demos because the library objects are now only built once.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>