phy: tegra: xusb: Add sleepwalk and suspend/resume

This commit adds sleepwalk/wake and suspend/resume interfaces
to Tegra XUSB PHY driver.

Tegra XUSB host controller driver makes use of sleepwalk functions
to enable/disable sleepwalk circuit which is in always-on partition
and can respond to USB resume signals when controller is not powered.
Sleepwalk can be enabled/disabled for any USB UPHY individually.

  - tegra_xusb_padctl_enable_phy_sleepwalk()
  - tegra_xusb_padctl_disable_phy_sleepwalk()

Tegra XUSB host controller driver makes use of wake functions to
enable/disable/query wake circuit which is in always-on partition
can wake system up when USB resume happens.
Wake circuit can be enabled/disabled for any USB PHY individually.

  - tegra_xusb_padctl_enable_phy_wake()
  - tegra_xusb_padctl_disable_phy_wake()
  - tegra_xusb_padctl_remote_wake_detected()

This commit also adds two system suspend stubs that can be used to
save and restore XUSB PADCTL context during system suspend and
resume.
  - tegra_xusb_padctl_suspend_noirq()
  - tegra_xusb_padctl_resume_noirq()

Signed-off-by: JC Kuo <jckuo@nvidia.com>
Acked-By: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>