net: davinci_emac: convert to using the driver model

Now that we removed all legacy boards selecting TI_EMAC we can
completely convert the driver code to using the driver model.
This patch also updates all remaining users of davinci_emac.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Tested-by: Adam Ford <aford173@gmail.com> #am3517-evm & da850-evm
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>