x86/jailhouse: Initialize PCI support

With this change, PCI devices can be detected and used inside a non-root
cell.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: jailhouse-dev@googlegroups.com
Link: https://lkml.kernel.org/r/e8d19494b96b68a749bcac514795d864ad9c28c3.1511770314.git.jan.kiszka@siemens.com