ARM: tegra: nyan: Maintain power to USB ports on boot

ARM: tegra: nyan: Maintain power to USB ports on boot

USB ports are turned on by the firmware as it looks for disks to boot,
ensure that they aren't power cycled before the xHCI driver comes up.

This enables USB devices to be ready for use faster and reduces wear
and risk of data loss on storage devices. A particularly annoying case
was booting from a mechanical disk, which takes time to spin up again.

Vendor kernel also kept these ports powered, and by the same means.

Signed-off-by: Michal Pecio <michal.pecio@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>