Adds a Phy Abstraction Layer which allows ethernet controllers to 
manage their PHYs without knowing the details of how the particular PHY 
device operates.  This code steals heavily from BenH's  sungem driver, 
and got some stuff out of Jason McMullan's patch.

Primary features of the code:
* Allows drivers to only use what they want (to a degree).  If you want 
to handle it all yourself, but use some of the data structures and 
functions, that's ok.  If you want to handle your own interrupts, 
that's fine.  However, it also allows you to minimize PHY management 
code.  See the gianfar driver patches (included for reference).
* Integrates with current ethtool/mii defined fields.
* Uses the driver model to manage binding PHY drivers to PHY devices, 
and MDIO bus drivers to MDIO bus devices.
* Doesn't affect drivers which don't use it.

Here's the patch: