usb: dwc3: ep0: add LPM handling

On device loading the driver enables LPM and the acceptance of U1 and U2
states. The [Set|Clear]Feature requests for "U1/U2" are forwarded
directly to the hardware and allow / forbid the initiation of the low
power links.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index dda56b8..906db57 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1933,6 +1933,7 @@
 
 	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
 	reg &= ~DWC3_DCTL_TSTCTRL_MASK;
+	reg &= ~(DWC3_DCTL_INITU1ENA | DWC3_DCTL_INITU2ENA);
 	dwc3_writel(dwc->regs, DWC3_DCTL, reg);
 	dwc->test_mode = false;
 
@@ -2330,6 +2331,14 @@
 		goto err5;
 	}
 
+	reg = dwc3_readl(dwc->regs, DWC3_DCFG);
+	reg |= DWC3_DCFG_LPM_CAP;
+	dwc3_writel(dwc->regs, DWC3_DCFG, reg);
+
+	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
+	reg |= DWC3_DCTL_ACCEPTU1ENA | DWC3_DCTL_ACCEPTU2ENA;
+	dwc3_writel(dwc->regs, DWC3_DCTL, reg);
+
 	/* Enable all but Start and End of Frame IRQs */
 	reg = (DWC3_DEVTEN_VNDRDEVTSTRCVEDEN |
 			DWC3_DEVTEN_EVNTOVERFLOWEN |