coreinfo: Skip unpopulated PCI functions

coreinfo: Skip unpopulated PCI functions

Per PCI specification, function 0 must be present,
so functions 1 to 7 can be skipped in this case.

For a device that is not multi-function, it may not
decode function number in the hardware at all. To
avoid registering such a device eight times, skip
scanning functions 1 to 7.

Without the latter fix, a single-function PCI bridge
may call pci_scan_bus() second time and secondary
side devices would get appended second time in the
array devices[]. At that point, quicksort() apparently
hits an infinite recursion loop.

Since pci_scan_bus() is called in part of the early
modules->init() sequence early in main(), the errors
here left coreinfo payload completely silent when
PCI module was built-in on affected system.

Terminal screen was cleared, though.

Change-Id: Ifc6622f050b98afb7196de0cc3a863c4cdfa6c94
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/26990
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>