KVM: s390: move bitmap idle_mask into arch struct top level

The vcpu idle_mask state is used by but not specific
to the emulated floating interruptions. The state is
relevant to gisa related interruptions as well.

Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Message-Id: <20190131085247.13826-4-mimu@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>