KVM: Add capability to advertise PSCI v0.2 support

User space (i.e. QEMU or KVMTOOL) should be able to check whether KVM
ARM/ARM64 supports in-kernel PSCI v0.2 emulation. For this purpose, we
define KVM_CAP_ARM_PSCI_0_2 in KVM user space interface header.

Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>