Adding mkabl to support MRB platforms (non signed kernel) and detection/rejection...

Adding mkabl to support MRB platforms (non signed kernel) and detection/rejection of configiguration with initrd=microcode.cpio

Change-Id: Iff7cbd34fb8abd0f0860fe183018a2d9a133614e
Signed-off-by: Dominig ar Foll Intel Open Source <dominig.arfoll@fridu.net>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/12669
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>