KVM: arm64: pvtime: Ensure task delay accounting is enabled

Ensure we're actually accounting run_delay before we claim that we'll
expose it to the guest. If we're not, then we just pretend like steal
time isn't supported in order to avoid any confusion.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200622142710.18677-1-drjones@redhat.com