ARM: realview: add EB syscon variants to bindings

There are two distinct RealView EB system controller that we need
to detect and handle because their register layout differ
slightly.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rob Herring <robh@kernel.org>