usb: dwc2: fix hang during suspend if set as peripheral

dwc2 on most platforms needs phy controller, clock and power supply.
All of them must be enabled/activated to properly operate. If dwc2
is configured as peripheral mode, then all the above three hardware
resources are disabled at the end of the probe:

/* Gadget code manages lowlevel hw on its own */
if (hsotg->dr_mode == USB_DR_MODE_PERIPHERAL)
dwc2_lowlevel_hw_disable(hsotg);

But the dwc2_suspend() tries to read the dwc2's reg to check whether
is_device_mode or not, this would result in hang during suspend if dwc2
is configured as peripheral mode.

Fix this hang by bypassing suspend/resume if lowlevel hw isn't
enabled.

Fixes: 09a75e857790 ("usb: dwc2: refactor common low-level hw code to platform.c")
Signed-off-by: Jisheng Zhang <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/dwc2/platform.c

···
 static int __maybe_unused dwc2_suspend(struct device *dev)
 {
 	struct dwc2_hsotg *dwc2 = dev_get_drvdata(dev);
-	bool is_device_mode = dwc2_is_device_mode(dwc2);
+	bool is_device_mode;
 	int ret = 0;
 
+	if (!dwc2->ll_hw_enabled)
+		return 0;
+
+	is_device_mode = dwc2_is_device_mode(dwc2);
 	if (is_device_mode)
 		dwc2_hsotg_suspend(dwc2);
 
···
 {
 	struct dwc2_hsotg *dwc2 = dev_get_drvdata(dev);
 	int ret = 0;
+
+	if (!dwc2->ll_hw_enabled)
+		return 0;
 
 	if (dwc2->phy_off_for_suspend && dwc2->ll_hw_enabled) {
 		ret = __dwc2_lowlevel_hw_enable(dwc2);