DaVinci: EMAC: Get EMAC_MDIO_PHY_NUM from config files

Currently EMAC_MDIO_PHY_NUM is defined as 1 in emac_defs.h.
Because of this, EMAC does not work on EVMs which do not have phy
connected at 1. Moving the macro to board config file makes this
configurable depending on where the phy is connected on the MDIO bus.

This patch fixes the board reset issue observed during network access
on DM365EVM. EMAC driver was assuming EMAC_MDIO_PHY_NUM as 1
but it is 0 on DM365EVM.

This patch is verified on da830/omap-l137, dm365 and dm644x evms.

Signed-off-by: Prakash PM <prakash.pm@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>