Revert "net: stmmac: allow to split suspend/resume from init/exit callbacks"

Instead of adding hooks inside stmmac_platform it is better to just use
the standard PM callbacks within the specific dwmac-driver. This only
used by the dwmac-rk driver.

This reverts commit cecbc556

 ("stmmac: allow to split suspend/resume
from init/exit callbacks").

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