irqchip/gic: Fix ARM11MPCore GIC bindings

The GIC bindings for the ARM11MPCore need to differentiate between
the GIC on the Test Chip and the one on the evaluation baseboard.
Split the binding in two and define new compatible-strings.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>