usb: dwc3: add u2exit lfps quirk

This patch adds u2exit lfps quirk, and some special platforms can configure
that if it is needed.

[ balbi@ti.com : added DeviceTree binding documentation ]

Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 6f9e5b85..33cbea5 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -473,6 +473,9 @@
 	else
 		reg &= ~DWC3_GCTL_DISSCRAMBLE;
 
+	if (dwc->u2exit_lfps_quirk)
+		reg |= DWC3_GCTL_U2EXIT_LFPS;
+
 	/*
 	 * WORKAROUND: DWC3 revisions <1.90a have a bug
 	 * where the device can fail to connect at SuperSpeed
@@ -729,6 +732,8 @@
 
 		dwc->disable_scramble_quirk = of_property_read_bool(node,
 				"snps,disable_scramble_quirk");
+		dwc->u2exit_lfps_quirk = of_property_read_bool(node,
+				"snps,u2exit_lfps_quirk");
 	} else if (pdata) {
 		dwc->maximum_speed = pdata->maximum_speed;
 		dwc->has_lpm_erratum = pdata->has_lpm_erratum;
@@ -739,6 +744,7 @@
 		dwc->dr_mode = pdata->dr_mode;
 
 		dwc->disable_scramble_quirk = pdata->disable_scramble_quirk;
+		dwc->u2exit_lfps_quirk = pdata->u2exit_lfps_quirk;
 	}
 
 	/* default to superspeed if no maximum_speed passed */