arm64: dts: add off-on-delay-us for usdhc2 regulator

arm64: dts: add off-on-delay-us for usdhc2 regulator

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.

To match such requirement on imx8qm-mek board, add 4.8ms delay between
sd power off and power on.

Fixes: 307fd14d4b14 ("arm64: dts: imx: add imx8qm mek support")
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>