PPC: KVM: store SLB slot number

When ppc_store_slb() is called from kvm_arch_get_registers(), it stores
a SLB in CPUPPCState::slb[slot]. However it drops the slot number from
ESID so when kvm_arch_put_registers() puts SLBs back to KVM, they do not
have correct "index" field anymore. This broke migration with LPCR_AIR
enabled as now the guest is handling interrupts in virtual mode and unable
to reconstruct correct SLBs anymore.

This adds "index" field for valid SLBs when putting them to KVM.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Alexander Graf <agraf@suse.de>
