Add ofw interface support to PCI

Some arm64 SoCs have nodes in their fdts that describe devices
connected to the internal PCI bus. One such SoC is Freescale LS1028A.
In order to access information stored in them we need to add ofw bus
support to pci. Pass devinfo request up to our parent, which
is responsible for parsing all the information.
It allows to use ofw interface on PCI devices that support it.
This method is similar to sys/dev/acpica/acpi_pci.c.

Submitted by: Kornel Duleba <mindal@semihalf.com>
Reviewed by: andrew
Obtained from: Semihalf
Sponsored by: Alstom Group
Differential Revision: https://reviews.freebsd.org/D30181