KVM: arm/arm64: vgic: Don't check vgic_initialized in sync/flush

Now when we do an early init of the static parts of the VGIC data
structures, we can do things like checking if the AP lists are empty
directly without having to explicitly check if the vgic is initialized
and reduce a bit of work in our critical path.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>