cpuidle: Don't enable all governors by default

Since commit d6f346f2

 (cpuidle: improve governor Kconfig options)
the best cpuidle governor is selected automatically. There is little
point in additionally selecting the other one as it will not be used,
so don't select both governors by default.

Being able to select more than one governor is still good for
developers booting with cpuidle_sysfs_switch, though.

This fixes the second half of kernel BZ #65531.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=65531
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>