PortioList is an abstraction used for construction of MemoryRegionPortioList
from MemoryRegionPortio. It can be used later to unmap created memory regions.
It also requires proper cleanup because some of the memory inside is allocated
dynamically.

By moving PortioList ot device state we make it possible to cleanup later and
avoid leaking memory.

This change spans several target platforms.  The following testcases cover all
changed lines:
  qemu-system-ppc -M prep
  qemu-system-i386 -vga qxl
  qemu-system-i386 -M isapc -soundhw adlib -device ib700,id=watchdog0,bus=isa.0

Signed-off-by: Kirill Batuzov <batuzovk@ispras.ru>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>