Allow DWC3 runtime suspend if UDC is unbinded

Changes in v2:
- Modified logic for executing the runtime PM resume. Using a sychronous get call to avoid race conditions.

During the following scenario, the DWC3 runtime suspend routine is blocked as the connected flag is still true:

1. Enumerate device w/ host.
2. Gadget is unbinded
- echo "" > /sys/kernel/config/usb_gadget/g1/UDC
3. Disconnect the USB cable (VBUS low)
4. No dwc3_gadget_disconnect_interrupt() seen (since controller is halted from step#1)
5. Runtime PM autosuspend fails due to "dwc->connected" being true (cleared in dwc3_gadget_disconnect_interrupt())
6. Gadget binded
- echo udc_name > /sys/kernel/config/usb_gadget/g1/UDC
7. No runtime suspend until cable is plugged in and out

Technically, for device initiated disconnects, there is no active session/link with the host, so the DWC3 controller should be allowed to go into a low power state. Also, we need to now consider when re-binding the UDC, dwc3_gadget_set_speed() is executed before dwc3_gadget_pullup(), so if the DWC3 controller is suspended/disabled, while accessing the DCFG, that could result in bus timeouts, etc... Change the dwc3_gadget_set_speed() to save the speed being requested, and program it during dwc3_gadget_run_stop(), which is executed during PM runtime resume. If not, previous setting will be overridden as we execute a DWC3 controller reset during PM runtime resume.

Wesley Cheng (2):
usb: dwc3: gadget: Allow runtime suspend if UDC unbinded
usb: dwc3: gadget: Preserve UDC max speed setting

 drivers/usb/dwc3/core.h   |   1 +
 drivers/usb/dwc3/gadget.c | 121 ++++++++++++++++++++++----------------
 2 files changed, 71 insertions(+), 51 deletions(-)

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