KVM: add kvm_arch_vcpu_runnable() test to kvm_vcpu_on_spin() loop

KVM: add kvm_arch_vcpu_runnable() test to kvm_vcpu_on_spin() loop

Use the arch specific function kvm_arch_vcpu_runnable() to add a further
criterium to identify a suitable vcpu to yield to during undirected yield
processing.

Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 98f4a14676127397c54cab7d6119537ed4d113a2)
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>