usb: phy: tegra: get ULPI reset GPIO info using DT.

As GPIO information is avail through DT, used it to get Tegra ULPI
reset GPIO number. Added a new member to tegra_usb_phy structure to
store this number.

Signed-off-by: Venu Byravarasu <vbyravarasu@nvidia.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>