sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Remove unused miibus_devclass and miibus_fdt_devclass.

mii_fdt: fix a set-but-not-used warning

bus_if: Add a default implementation of get_property

There are multiple buses that pretend to be ofw compatible,
e.g ofw_pci, mii_fdt. We now need to provide an implementation
of BUS_GET_PROPERTY for every one of them. Instead of modifying
them one by one it's better to just provide a default
implementation that simply traverses up the device tree.
Remove the now unneeded BUS_GET_PROPERTY implementation in mii_fdt.

Reviewed by: andrew, bz
Obtained from: Semihalf
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D34031

miibus: Add support for mapping OFW nodes to PHY devices

Create a new miibus OFW specific layer leveraging miibus_fdt.c code.
PHY drivers can than read the properties using device_get_property(9) API.
Resource(interrupt) allocation is also supported.
In order to enable this each NIC/switch driver will have to be modified,
because of how miibus is attached to the parent driver.

Obtained from: Semihalf
Sponsored by: Alstom Group
Differential revision: https://reviews.freebsd.org/D32812

mii_fdt: Add support for switch PHY node lookup

Previously we would only search for a PHY xref in node of the miibus
parent.
That didn't work very well with switches.
Fix that by searching through "ports" subnode, checking if any of its
children have a valid PHY xref.
Since switches tend to have multiple ports we also have multiple
candidates.
Use the PHY address read from mii_attach_args to find the right one.

Obtained from: Semihalf
Sponsored by: Alstom Group
Reviewed by: mw
Differential revision: https://reviews.freebsd.org/D32690

Add some utility functions to help a PHY driver on an FDT-configured
system retrieve its config data from the fdt data.

The properties that are common to all phys are decoded and returned in a
structure. The fdt node handles for the mac and phy devices are also
returned in the config data struct, so a driver can easily obtain additional
hardware-specific config values from the fdt data.