cpufreq: amd-pstate: Set default governor to schedutil

The Kconfig currently defaults the governor to schedutil on x86_64
only when intel-pstate and SMP have been selected.

If the kernel is built only with amd-pstate, the default governor
should also be schedutil.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Tested-by: Perry Yuan <Perry.Yuan@amd.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>