davinci: emac: add support for more than 1 PHYs

add support for more than 1 PHYs. Many of the davinci platforms have more
than 1 PHYs on thier board. This patch extends support in davinci emac
driver for upto 3 PHYs.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>