ARM: davinci: fix clock lookup for mdio device

This patch removes the clock alias for mdio device and adds a entry
in clock lookup table, this entry can now be used by both DT and
non-DT case.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>