doc: dt: bindings: usb: dwc3: Update entries for disabling SS instances in park mode

This patch updates the documentation with the information related
to the quirks that needs to be added for disabling all SuperSpeed XHCI
instances in park mode.

Cc: Dongjin Kim <tobetter@gmail.com>
Cc: Jianxin Pan <jianxin.pan@amlogic.com>
Cc: Thinh Nguyen <thinhn@synopsys.com>
Cc: Jun Li <lijun.kernel@gmail.com>
Reported-by: Tim <elatllat@gmail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

Documentation/devicetree/bindings/usb/dwc3.txt

@@ -75,6 +75,8 @@ Optional properties:
 			from P0 to P1/P2/P3 without delay.
  - snps,dis-tx-ipgap-linecheck-quirk: when set, disable u2mac linestate check
 			during HS transmit.
+ - snps,parkmode-disable-ss-quirk: when set, all SuperSpeed bus instances in
+			park mode are disabled.
  - snps,dis_metastability_quirk: when set, disable metastability workaround.
 			CAUTION: use only if you are absolutely sure of it.
  - snps,is-utmi-l1-suspend: true when DWC3 asserts output signal