nvidia: Update Tegra186 XUSB firmware to v55.18

Update firmware file for the XUSB controller found on Tegra186.
This is version 55.18 of the Tegra186 XUSB firmware.

Signed-off-by: JC Kuo <jckuo@nvidia.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>