dsa: Move gpio reset into switch driver

Resetting the switch is something the driver does, not the framework.
So move the parsing of this property into the driver.

There are no in kernel users of this property, so moving it does not
break anything. There is however a board which will make use of this
property making its way into the kernel.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>