kvmtool: ARM/ARM64: Provide PSCI-0.2 to guest when KVM supports it

If in-kernel KVM support PSCI-0.2 emulation then we should set
KVM_ARM_VCPU_PSCI_0_2 feature for each guest VCPU and also
provide "arm,psci-0.2","arm,psci" as PSCI compatible string.

This patch updates kvm_cpu__arch_init() and setup_fdt() as
per above.

Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>