integrator: convert to new build system

This deletes the integrator split_by_variant.sh script and
defines a number of unique board types for the core modules
that are meaningful to support for the Integrator AP/CP, i.e.
the ones that did not just say "unsupported core module" in
split_by_variant.sh. If more core modules need to be supported
they are easy to add.

We delete all the old cruft in Makefile and MAKEALL that was
working around the old way of building boards. We create a
unique config file per board to satisfy the build system, but
they are just oneliners that include the existing
integratorap.h and integratorcp.h configs.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>