stmmac: dwmac-rk: absorb rk_gmac_init into probe

Since the rk_gmac_init() only calls another function move this
function call into probe so rk_gmac_init() can be removed.

Since commit cecbc556 ("stmmac: allow to split suspend/resume
from init/exit callbacks") the init hook is no longer used in
dwmac-rk so this can be removed.

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