usb: host: xhci-tegra: Add XUSB controller context

Define the offsets of the registers that need to be saved on suspend and
restored on resume for the various NVIDIA Tegra generations supported by
the XUSB driver.

Based on work by JC Kuo <jckuo@nvidia.com>.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20191206140653.2085561-10-thierry.reding@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>