phy: tegra: xusb: Add Tegra194 support

Add support for the XUSB pad controller found on Tegra194 SoCs. It is
mostly similar to the same IP found on Tegra186, but the number of
pads exposed differs, as do the programming sequences. Because most of
the Tegra194 XUSB PADCTL registers definition and programming sequence
are the same as Tegra186, Tegra194 XUSB PADCTL can share the same
driver, xusb-tegra186.c, with Tegra186 XUSB PADCTL.

Tegra194 XUSB PADCTL supports up to USB 3.1 Gen 2 speed, however, it
is possible for some platforms have long signal trace that could not
provide sufficient electrical environment for Gen 2 speed. This patch
adds a "maximum-speed" property to usb3 ports which can be used to
specify the maximum supported speed for any particular USB 3.1 port.
For a port that is not capable of SuperSpeedPlus, "maximum-speed"
property should carry "super-speed".

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