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

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

Since commit:

    048e3a34a2e7 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: 048e3a34a2e7 ("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>