siemens/mc_apl3: Add new mainboard variant mc_apl3

siemens/mc_apl3: Add new mainboard variant mc_apl3

This mainboard is based on mc_apl1. In a first step, it concerns a copy
of mc_apl1 directory with minimum changes. Special adaptations for
mc_apl3 mainboard will follow in separate commits.

Change-Id: I963ec63bccf71296c3fdabfcf9f3009c2febc791
Signed-off-by: Mario Scheithauer <mario.scheithauer@siemens.com>
Reviewed-on: https://review.coreboot.org/29353
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>