ARM: defconfig: u8500: activate cpufreq

This activates the device tree-based cpufreq driver that
Ux500 is using and enables the schedutil and ondemand
governors with schedutil as default. This works fine in
the setups I have tested.

Link: https://lore.kernel.org/r/20191217202648.23206-1-linus.walleij@linaro.org
Cc: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>