[POWERPC] Generalize tsi108 PHY types

Add a phy_type field to the tsi108 ethernet structures to indicate which PHY
is used on a board.  This is derived from the "compatible" property in the
ethernet-phy node of the device tree.  The default remains the MV88E PHY.

Also, convert the setup code to use of_get_mac_address instead of hard coding
a lookup for the "address" property in the ethernet node.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>