stmmac: export probe_config_dt() and get_platform_resources()

Export stmmac_probe_config_dt() and stmmac_get_platform_resources()
so they can be used in the dwmac-* drivers themselves. This will
allow us to build more flexible and standalone drivers which just
use stmmac_platform as a library for setup functions.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>