net: smc91x: Fix gpios for device tree based booting

With legacy booting, the platform init code was taking care of
the configuring of GPIOs. With device tree based booting, things
may or may not work depending what bootloader has configured or
if the legacy platform code gets called.

Let's add support for the pwrdn and reset GPIOs to the smc91x
driver to fix the issues of smc91x not working properly when
booted in device tree mode.

And let's change n900 to use these settings as some versions
of the bootloader do not configure things properly causing
errors.

Reported-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: David S. Miller <davem@davemloft.net>