s390x/cpumodel: register defined CPU models as subclasses

This patch adds the CPU model definitions that are known on s390x -
like z900, zBC12 or z13. For each definition, introduce two CPU models:

1. Base model (e.g. z13-base): Minimum feature set we expect to be around
   on all z13 systems. These models are migration-safe and will never
   change.
2. Flexible models (e.g. z13): Models that can change between QEMU versions
   and will be extended over time as we implement further features that
   are already part of such a model in real hardware of certain
   configurations.

We want to work on features using ordinary bitmap operations, however we
can't initialize a bitmap statically (unsigned long[] ...). Therefore we
store the generated feature lists in separate arrays and convert them to
proper bitmaps before registering all our CPU model classes.

Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Message-Id: <20160905085244.99980-9-dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
