ewaol-distro/ewaol-image-core: Include build info into the images

By inheriting image-buildinfo the EWAOL images will include the /etc/build file
which contains information about the build configuration as well as the layers
revisions.

Issue-Id: SCM-3910
Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Change-Id: I61a80628ed9decd8701a8e793444dfb9d03bccfa