davinci: DA850/OMAP-L138 EVM: simplify configuration of emac in MII/RMII mode

There are multiple steps in configuring the EMAC to MII or RMII mode.
Current code implements them using multiple checks.

Consolidate the multiple checks into a single if construct.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>