usb: dwc3: xilinx: Skip resets and USB3 register settings for USB2.0 mode

usb: dwc3: xilinx: Skip resets and USB3 register settings for USB2.0 mode

It appears that the PIPE clock should not be selected when only USB 2.0
is being used in the design and no USB 3.0 reference clock is used.
Also, the core resets are not required if a USB3 PHY is not in use, and
will break things if USB3 is actually used but the PHY entry is not
listed in the device tree.

Skip core resets and register settings that are only required for
USB3 mode when no USB3 PHY is specified in the device tree.

Fixes: 84770f028fab ("usb: dwc3: Add driver for Xilinx platforms")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Link: https://lore.kernel.org/r/20220126000253.1586760-2-robert.hancock@calian.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>