Add a new get_id interface to pci and pcib. This will allow us to both
detect failures, and get different PCI IDs.

For the former the interface returns an int to signal an error. The ID is
returned at a uintptr_t * argument.

For the latter there is a type argument that allows selecting the ID type.
This only specifies a single type, however a MSI type will be added
to handle the need to find the ID the hardware passes to the ARM GICv3
interrupt controller.

A follow up commit will be made to remove pci_get_rid.

Reviewed by: jhb, rstone
Obtained from: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D6239