fsl: Change fsl_phy_enet_if to phy_interface_t

The fsl_phy_enet_if enum was, essentially, the phy_interface_t enum.
This meant that drivers which used fsl_phy_enet_if to deal with
PHY interfaces would have to convert between the two (or we would have
to have them mirror each other, and deal with the ensuing maintenance
headache). Instead, we switch all clients of fsl_phy_enet_if over to
phy_interface_t, which should become the standard, anyway.

Signed-off-by: Andy Fleming <afleming@freescale.com>
Acked-by: Detlev Zundel <dzu@denx.de>