ARM: tegra: add USB ULPI PHY reset GPIO to device tree
ULPI PHYs have a reset signal, and different boards use a different GPIO
for this task. Add a property to device tree to represent this.
I'm not sure if adding this property to the EHCI controller node is
entirely correct; perhaps eventually we should have explicit separate
nodes for the various PHYs. However, we don't have that right now, so this
binding seems like a reasonable choice.