mel: exclude FSL_EULA_FILE, IVI_COREBASE

These variables are full absolute paths into layers. Without excluding them
from the signatures, we end up not being able to reuse those sstates if the
path to meta-fsl-arm and meta-ivi change.

Add them to vardepsexclude where appropriate.

JIRA: MEIP-165, SB-1462

Signed-off-by: Christopher Larson <kergoth@gmail.com>