Documentation: dt: dwc3: Add snps,quirk-frame-length-adjustment property

Add snps,quirk-frame-length-adjustment property which provides value
for post silicon frame length adjustment

Signed-off-by: Nikhil Badola <nikhil.badola@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

Documentation/devicetree/bindings/usb/dwc3.txt

@@ -40,6 +40,9 @@ Optional properties:
  - snps,hird-threshold: HIRD threshold
  - snps,hsphy_interface: High-Speed PHY interface selection between "utmi" for
    UTMI+ and "ulpi" for ULPI when the DWC_USB3_HSPHY_INTERFACE has value 3.
+ - snps,quirk-frame-length-adjustment: Value for GFLADJ_30MHZ field of GFLADJ
+	register for post-silicon frame length adjustment when the
+	fladj_30mhz_sdbnd signal is invalid or incorrect.
 
 This is usually a subnode to DWC3 glue to which it is connected.