cpufreq: amd-pstate: Set a fallback policy based on preferred_profile

If a user's configuration doesn't explicitly specify the cpufreq
scaling governor then the code currently explicitly falls back to
'powersave'. This default is fine for notebooks and desktops, but
servers and undefined machines should default to 'performance'.

Look at the 'preferred_profile' field from the FADT to set this
policy accordingly.

Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html#fixed-acpi-description-table-fadt


Acked-by: Huang Rui <ray.huang@amd.com>
Suggested-by: Wyes Karny <Wyes.Karny@amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>