arm64: dts: imx8mn-evk: change to use off-on-delay-us in regulator

arm64: dts: imx8mn-evk: change to use off-on-delay-us in regulator

After commit f7907e57aea2 ("regulator: fixed: add off-on-delay"), user
can use "off-on-delay-us" to define the regulator off-delay time.

For SD card, according to the spec requirement, for sd card power reset
operation, it need sd card supply voltage to be lower than 0.5v and keep
over 1ms, otherwise, next time power back the sd card supply voltage to
3.3v, sd card can't support SD3.0 mode again.

This patch add the off-on-delay-us to each board, make sure the sd power
reset behavior is align with the specification. Without this patch, when
do quick system suspend/resume test, some sd card can't work at SD3.0 mode
after system resume back.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>