ARM: davinci: da850-evm: use GPIO hogs instead of the legacy API

In order to drop the hard-coded GPIO base values from the davinci GPIO
driver's platform data, we first need to get rid of all calls to the
legacy GPIO functions. Convert the mdio configuration to hogging the
relevant GPIO line in the da850-evm board file.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>