KVM: arm64: vgic-v3: Log which GICv3 system registers are trapped

In order to facilitate debug, let's log which class of GICv3 system
registers are trapped.

Tested-by: Alexander Graf <agraf@suse.de>
Acked-by: David Daney <david.daney@cavium.com>
Acked-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>