PCI: Scan all functions when running over Jailhouse

Per PCIe r4.0, sec 7.5.1.1.9, multi-function devices are required to have a
function 0.  Therefore, Linux scans for devices at function 0 (devfn
0/8/16/...) and only scans for other functions if function 0 has its
Multi-Function Device bit set or ARI or SR-IOV indicate there are more
functions.

The Jailhouse hypervisor may pass individual functions of a multi-function
device to a guest without passing function 0, which means a Linux guest
won't find them.

Change Linux PCI probing so it scans all function numbers when running as a
guest over Jailhouse.

This is technically prohibited by the spec, so it is possible that PCI
devices without the Multi-Function Device bit set may have unexpected
behavior in response to this probe.

Originally-by: Benedikt Spranger <[email protected]>
Signed-off-by: Jan Kiszka <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Acked-by: Bjorn Helgaas <[email protected]>
Cc: [email protected]
Cc: Benedikt Spranger <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/06e279b2a3e06cf6689ab3975f8ab592bba02362.1520408357.git.jan.kiszka@siemens.com

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