NET: dwmac: Make dwmac reset unconditional

Unconditional reset dwmac before HW init if reset controller is present.

In existing implementation we reset dwmac only after second module
probing:
(module load -> unload -> load again [reset happens])

Now we reset dwmac at every module load:
(module load [reset happens] -> unload -> load again [reset happens])

Also some reset controllers have only reset callback instead of
assert + deassert callbacks pair, so handle this case.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>