To support having more than one layer in Arm Automotive Solutions, split
out the parts specific to meta-arm-auto-solutions into its own YAML
file. This ensures that all layers build with the same revisions and
patches.

base.yml now declares poky explicitly (which was previously defined by
meta-cassini). meta-openembbeded only defines meta-oe by default.

Rename all references to base.yml to arm-auto-solutions.yml

Signed-off-by: Peter Hoyes <peter.hoyes@arm.com>