arm/dt: add basic usb nodes to tegra device trees

For now they are a minimal binding. It needs to be amended with
vendor-specific settings for phy setup and link tuning, etc.

v2: Added bindings specification and phy_type properties

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Stephen Warren <swarren@nvidia.com>