hw/arm/virt: Allow virt extensions with KVM

hw/arm/virt: Allow virt extensions with KVM

Up to now virt support on guest has been only supported with TCG.
Now it becomes feasible to use it with KVM acceleration.

Check neither in-kernel GICv3 nor aarch64=off is used along with KVM
EL2.

Signed-off-by: Haibo Xu <haibo.xu@linaro.org>
Signed-off-by: Miguel Luis <miguel.luis@oracle.com>
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250707164129.1167837-6-eric.auger@redhat.com
[PMM: make "kernel doesn't have EL2 support" error message
 distinct from the old "QEMU doesn't have KVM EL2 support" one]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>