msm: emac: factor out phy abstraction layer

Create an abstract phy layer over the sgmii and rgmii modules.
This cleanly splits the functionality between mac and phy layers
into separate source files.

Change-Id: I7c2a052376c530659b9b35f6edf7b18c1dd60b9a
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>