hw/intc/arm_gicv3_kvm: Check KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS in reset

KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS needs to be checked before
attempting to read ICC_CTLR_EL1; otherwise kernel versions not
exposing this kvm device group will be incompatible with qemu 2.9.

Fixes: 07a5628  ("hw/intc/arm_gicv3_kvm: Reset GICv3 cpu interface registers")
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reported-by: Prakash B <bjsprakash.linux@gmail.com>
Tested-by: Alexander Graf <agraf@suse.de>
Message-id: 1490721640-13052-1-git-send-email-eric.auger@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
