arm64: defconfig: ARM_IMX_CPUFREQ_DT=m

For imx8m we need a separate small driver to read "speed grading"
information from fuses and determine which OPPs are supported.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>