usb: dwc2: Add clock gating entering flow by system suspend

If not hibernation nor partial power down are supported,
clock gating is used to save power.

Adds a new flow of entering clock gating when PC is
suspended.
Signed-off-by: Artur Petrosyan <Arthur.Petrosyan@synopsys.com>
Link: https://lore.kernel.org/r/20210413073716.30C13A0094@mailhost.synopsys.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc2/hcd.c

@@ -4372,6 +4372,15 @@ static int _dwc2_hcd_suspend(struct usb_hcd *hcd)
 		break;
 	case DWC2_POWER_DOWN_PARAM_HIBERNATION:
 	case DWC2_POWER_DOWN_PARAM_NONE:
+		/*
+		 * If not hibernation nor partial power down are supported,
+		 * clock gating is used to save power.
+		 */
+		dwc2_host_enter_clock_gating(hsotg);
+
+		/* After entering suspend, hardware is not accessible */
+		clear_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);
+		break;
 	default:
 		goto skip_power_saving;
 	}