net: qcom/emac: move phy init code to separate files

The internal PHY of the EMAC differs on each SOC, and the list will
only continue to grow.  By separating the code into individual files,
we can add support for more SOCs more cleanly.

Note: The internal PHY is also sometimes called the SGMII device.

We also stop referring to the various PHY variations by version number,
so no more "v2", "v3", etc.  Instead, the devices are named after the
SOC they are, which is in sync with the device tree property names.

Future patches will probably rearrange more code among the files.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>