dt-bindings: usb: dwc3: Add disabling LPM for gadget

Add a new DT option to disable LPM for gadget and update the description
for usb2-lpm-disable related to host for clarity.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/f31348ba744318c83b3a9ab1eab75c61122b15ae.1618366071.git.Thinh.Nguyen@synopsys.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/snps,dwc3.yaml

@@ -87,13 +87,19 @@ properties:
     minItems: 1
 
   snps,usb2-lpm-disable:
-    description: Indicate if we don't want to enable USB2 HW LPM
+    description: Indicate if we don't want to enable USB2 HW LPM for host
+      mode.
     type: boolean
 
   snps,usb3_lpm_capable:
     description: Determines if platform is USB3 LPM capable
     type: boolean
 
+  snps,usb2-gadget-lpm-disable:
+    description: Indicate if we don't want to enable USB2 HW LPM for gadget
+      mode.
+    type: boolean
+
   snps,dis-start-transfer-quirk:
     description:
       When set, disable isoc START TRANSFER command failure SW work-around