ARM: integrator: core module registers from compatible strings

This augments the core machine code for the Integrator platforms
to get their references to the core module device nodes by
using compatible strings instead of predefined node names
and rename the CP syscon node to be simply "syscon".

Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>