Add a matching set of device_ functions for determining mac/phy

OF has some helper functions for parsing MAC and PHY settings.
In cases where the platform is providing this information rather
than the device itself, there needs to be similar functions for ACPI.

These functions are slightly modified versions of the ones in
of_net which can use information provided via DT or ACPI.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>