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/core.h b/drivers/usb/dwc3/core.h
index c7b3ca0..93f9973 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -194,6 +194,7 @@
 #define DWC3_GHWPARAMS1_EN_PWROPT_CLK	1
 
 /* Device Configuration Register */
+#define DWC3_DCFG_LPM_CAP	(1 << 22)
 #define DWC3_DCFG_DEVADDR(addr)	((addr) << 3)
 #define DWC3_DCFG_DEVADDR_MASK	DWC3_DCFG_DEVADDR(0x7f)