phy: tegra: xusb: Add wake/sleepwalk for Tegra210

This commit implements Tegra210 XUSB PADCTL wake and sleepwalk
routines. Sleepwalk logic is in PMC (always-on) hardware block.
PMC driver provides managed access to the sleepwalk registers
via regmap framework.
Signed-off-by: JC Kuo <jckuo@nvidia.com>
Acked-By: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>