devfreq: imx8m-ddrc: Add late system sleep PM ops

Seems that, in order to be able to resume from suspend, the dram rate
needs to be the highest one available. Therefore, add the late system
suspend/resume PM ops which set the highest rate on suspend and the
latest one used before suspending on resume.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
2 jobs for devfreq_suspend in 92 minutes and 5 seconds (queued for 2 seconds)
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