[S390] remove kvm mmu reload on s390

This patch removes the mmu reload logic for kvm on s390. Via Martin's
new gmap interface, we can safely add or remove memory slots while
guest CPUs are in-flight. Thus, the mmu reload logic is not needed
anymore.

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>