x86/jailhouse: Enable PCI mmconfig access in inmates

Use the PCI mmconfig base address exported by jailhouse in boot parameters
in order to access the memory mapped PCI configuration space.

[Jan: rebased, fixed !CONFIG_PCI_MMCONFIG, used pcibios_last_bus]

Signed-off-by: Otavio Pontes <otavio.pontes@intel.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: jailhouse-dev@googlegroups.com
Cc: linux-pci@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Cc: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lkml.kernel.org/r/2ee9e4401fa22377b3965893a558120f169be82b.1520408357.git.jan.kiszka@siemens.com