usb: gadget: tegra-xudc: Use phy_set_mode() to set/unset device mode

When device mode is set/unset, VBUS override activity is done via
exported functions from padctl driver. Use phy_set_mode() instead.

Signed-off-by: Nagarjuna Kristam <nkristam@nvidia.com>
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>