net: qcom/emac: rename emac_phy to emac_sgmii and move it

The EMAC has an internal PHY that is often called the "SGMII".  This
SGMII is also connected to an external PHY, which is managed by phylib.
These dual PHYs often cause confusion.  In this case, the data structure
for managing the SGMII was mis-named and located in the wrong header file.

Structure emac_phy is renamed to emac_sgmii to clearly indicate it applies
to the internal PHY only.  It also also moved from emac_phy.h (which
supports the external PHY) to emac_sgmii.h (where it belongs).

To keep the changes minimal, only the structure name is changed, not
the names of any variables of that type.

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