LF-6808: arm64: dts: imx8mp-evk: switch MCLK from SoC to external 24M oscillator for OS08A20

According to FCC certification test results, we may need to disable MCLK
output from IMX8MPlus EVK board and switch MCLK from SoC external 24M oscillator
on the camera modules for OS08A20. And there are two options for sensor’s MCLK
on the camera module, default option is using MCLK from i.MX8MPlus, and in
this case hardware can’t pass FCC certification. Another is use 24M oscillator
on the camera module, this can pass the FCC certification.

Please refer to HW ticket number: MXEMPLUS-24

Signed-off-by: Alice Yuan <alice.yuan@nxp.com>
Reviewed-by: Robby Cai <robby.cai@nxp.com>