TYPE_IOMMU_MEMORY_REGION is a direct subtype of TYPE_MEMORY_REGION.
Its instance struct is IOMMUMemoryRegion, and its first member is a
MemoryRegion.  Correct.  Its class struct is IOMMUMemoryRegionClass,
and its first member is a DeviceClass.  Wrong.  Messed up when commit
1221a474 introduced the QOM type.  It even included hw/qdev-core.h
just for that.

TYPE_MEMORY_REGION doesn't bother to define a class struct.  This is
fine, it simply defaults to its super-type TYPE_OBJECT's class struct
ObjectClass.  Changing IOMMUMemoryRegionClass's first member's type to
ObjectClass would be a minimal fix, if a bit brittle: if
TYPE_MEMORY_REGION ever acquired own class struct, we'd have to update
IOMMUMemoryRegionClass to use it.

Fix it the clean and robust way instead: give TYPE_MEMORY_REGION its
own class struct MemoryRegionClass now, and use it for
IOMMUMemoryRegionClass's first member.

Revert the include of hw/qdev-core.h, and fix the few files that have
come to rely on it.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20190812052359.30071-5-armbru@redhat.com>