usb: dwc3: add lfps filter quirk

This patch adds LFPS filter 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 de6a009..29a7da0 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -386,6 +386,9 @@
 	if (dwc->del_phy_power_chg_quirk)
 		reg |= DWC3_GUSB3PIPECTL_DEPOCHANGE;
 
+	if (dwc->lfps_filter_quirk)
+		reg |= DWC3_GUSB3PIPECTL_LFPSFILT;
+
 	dwc3_writel(dwc->regs, DWC3_GUSB3PIPECTL(0), reg);
 
 	mdelay(100);
@@ -771,6 +774,8 @@
 				"snps,del_p1p2p3_quirk");
 		dwc->del_phy_power_chg_quirk = of_property_read_bool(node,
 				"snps,del_phy_power_chg_quirk");
+		dwc->lfps_filter_quirk = of_property_read_bool(node,
+				"snps,lfps_filter_quirk");
 	} else if (pdata) {
 		dwc->maximum_speed = pdata->maximum_speed;
 		dwc->has_lpm_erratum = pdata->has_lpm_erratum;
@@ -786,6 +791,7 @@
 		dwc->req_p1p2p3_quirk = pdata->req_p1p2p3_quirk;
 		dwc->del_p1p2p3_quirk = pdata->del_p1p2p3_quirk;
 		dwc->del_phy_power_chg_quirk = pdata->del_phy_power_chg_quirk;
+		dwc->lfps_filter_quirk = pdata->lfps_filter_quirk;
 	}
 
 	/* default to superspeed if no maximum_speed passed */