ARM: mxs_defconfig: Enable cpufreq-dt

Enable cpufreq-dt with voltage scaling built by default.

Generated by doing:

make mxs_defconfig
Manually selected CONFIG_POWER_SUPPLY and CONFIG_MXS_POWER driver
Manually selected CONFIG_REGULATOR_MXS driver
Manually selected CONFIG_CPU_FREQ and CONFIG_CPUFREQ_DT driver
make savedefconfig
cp defconfig arch/arm/configs/mxs_defconfig

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>