soc/tegra: pmc: Provide USB sleepwalk register map

This commit implements a register map which grants USB (UTMI and HSIC)
sleepwalk registers access to USB PHY drivers. The USB sleepwalk logic
is in PMC hardware block but USB PHY drivers have the best knowledge
of proper programming sequence.

Signed-off-by: JC Kuo <jckuo@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>