ARM: dts: imx6/7: sync fsl,stop-mode with current flexcan driver

After this patch we need 2 arguments less for the fsl,stop-mode
property:

| commit d9b081e3
| Author: Marc Kleine-Budde <mkl@pengutronix.de>
| Date:   Sun Jun 14 21:09:20 2020 +0200
|
| can: flexcan: remove ack_grp and ack_bit handling from driver
|
| 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. This patch removes the used "ack_gpr" and "ack_bit" from the driver.

This patch removes the two last arguments, as they are not needed
anymore.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>