pci: Turn struct pci_dev into device handle for PCI functions

Currently struct pci_dev is used for caching PCI device
info used by some functions. This update turns the struct
into device handle that will be used by nearly all existing
and future APIs.

As result of this change a pci_dev should be initialized
with pci_dev_init() and pci_scan_bars() becomes redundant.

Cc: Thomas Huth <thuth@redhat.com>
Cc: Andrew Jones <drjones@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>