igc: Support ACPI-based MAC passthrough

Some systems implement a system MAC address object in the ACPI table,
using either \\_SB.AMAC or \\MACA object names. This system MAC address,
when enabled, is intended to override the permanent MAC address of the
any network controller attached via a docking station. The purpose is to
allow the host PC retain its network identity in a corporate environment,
regardless of the specific docking station it is connected to. The
expectation is that only one docking station is attached at a time, or
that only a single network controller is plugged in at a time.

Implement seamless passthrough of the system MAC address to the
I225/I226 network controller, by looking up the relevant ACPI object names
and using them to initialize the MAC address. Limit the lookup only to
controllers that are Thunderbolt-attached, as these are the only docking
stations that can pass through an I225/I226 controller to the host.

On systems where the feature is disabled or unsupported, the ACPI objects
do not exist or do not contain a valid Ethernet MAC, the default MAC
address of the device is used.

Assisted-by: GitHub-Copilot:claude-opus-4.7
Signed-off-by: Dima Ruinskiy <dima.ruinskiy@intel.com>