irqchip/gic-v3: Parse and export virtual GIC information

Fill up the recently introduced gic_kvm_info with the hardware
information used for virtualization.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>