dt-bindings: can: flexcan: remove ack_grp and ack_bit from fsl,stop-mode

Since commit:

    048e3a34 can: flexcan: poll MCR_LPM_ACK instead of GPR ACK for stop mode acknowledgment

the driver polls the IP core's internal bit MCR[LPM_ACK] as stop mode
acknowledge and not the acknowledgment on chip level.

This means the 4th and 5th value of the property "fsl,stop-mode" isn't used
anymore. It will be removed from the driver in the next patch, so remove it
from the binding documentation.

Link: http://lore.kernel.org/r/20201006203748.1750156-14-mkl@pengutronix.de
Fixes: 048e3a34 ("can: flexcan: poll MCR_LPM_ACK instead of GPR ACK for stop mode acknowledgment")
Cc: devicetree <devicetree@vger.kernel.org>
Cc: Joakim Zhang <qiangqing.zhang@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/fsl-flexcan.txt

@@ -31,12 +31,10 @@ Optional properties:
               endian.
 
 - fsl,stop-mode: register bits of stop mode control, the format is
-		 <&gpr req_gpr req_bit ack_gpr ack_bit>.
+		 <&gpr req_gpr req_bit>.
 		 gpr is the phandle to general purpose register node.
 		 req_gpr is the gpr register offset of CAN stop request.
 		 req_bit is the bit offset of CAN stop request.
-		 ack_gpr is the gpr register offset of CAN stop acknowledge.
-		 ack_bit is the bit offset of CAN stop acknowledge.
 
 - fsl,clk-source: Select the clock source to the CAN Protocol Engine (PE).
 		  It's SoC Implementation dependent. Refer to RM for detailed