arm64: defconfig: Enable devfreq support for i.MX8MQ

This is needed to make DRAM frequency scaling via devfreq as used
on the Librem 5 and Librem 5 Devkit.

With the interconnect support enabled we now need imx devfreq on top
to make this work.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>