PCI: replace stray uses of PCI_{DEVFN,BDF}2()

PCI: replace stray uses of PCI_{DEVFN,BDF}2()

There's no good reason to use these when we already have a pci_sbdf_t
type object available. This extends to the use of PCI_BUS() in
pci_ecam_map_bus() as well.

No change to generated code (with gcc11 at least, and I have to admit
that I didn't expect compilers to necessarily be able to spot the
optimization potential on the original code).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>