pc: Unbreak ROM mapping for ISA machine This is based on the original fix by Hervé Poussineau: pc_memory_init actually takes a memory region for mapping BIOS and extension ROMs. That equals the PCI memory region if PCI is available, but must be system memory in the ISA case. Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>