KVM: arm/arm64: Advertise support for KVM_CAP_ARM_USER_IRQ

Now that we support both timers and PMU reporting interrupts
to userspace, we can advertise this support.

Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>