target/arm/kvm: Let kvm_arm_vgic_probe() return a bitmap

target/arm/kvm: Let kvm_arm_vgic_probe() return a bitmap

Convert kvm_arm_vgic_probe() so that it returns a
bitmap of supported in-kernel emulation VGIC versions instead
of the max version: at the moment values can be v2 and v3.
This allows to expose the case where the host GICv3 also
supports GICv2 emulation. This will be useful to choose the
default version in KVM accelerated mode.

Signed-off-by: Eric Auger <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-id: 20200311131618[email protected]
Signed-off-by: Peter Maydell <[email protected]>