[DRIVERS] net: Linux compatible PHY, MDIO, and MII framework

This patch does the following:
1. Reorganize drivers/net directory
2. Add experimental MII framework
3. Add experimental MDIO framework
4. Add experimental network PHY framework

Lot of network drivers depend on PHY, MDIO, and MII APIs. This
patch ports these frameworks and APIs from Linux 3.12.6.

Signed-off-by: Pranav Sawargaonkar <pranav.sawargaonkar@gmail.com>