ARM: KVM: Convert KVM to use HVC_GET_VECTORS

The conversion of the HYP stub ABI to something similar to arm64
left the KVM code broken, as it doesn't know about the new
stub numbering. Let's move the various #defines to virt.h, and
let KVM use HVC_GET_VECTORS.

Tested-by: Keerthy <j-keerthy@ti.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>