ipq806x: compile in schedutil governor

ipq806x: compile in schedutil governor

Gives users a third option to augment ondemand and performance. Kernel
docs[1] explain differences and this PR empowers users w/ the choice to
select between the older ondemand and newer and more simplistic schedutil
should they wish to use one that is not the performance governor.

1. Documentation/admin-guide/pm/cpufreq.rst

Signed-off-by: John Audia <graysky@archlinux.us>
[fixed From: to match SoB:]
Signed-off-by: Petr Štetiar <ynezz@true.cz>