cpufreq: amd-pstate: Add AMD P-State frequencies attributes

cpufreq: amd-pstate: Add AMD P-State frequencies attributes

BugLink: https://bugs.launchpad.net/bugs/1956509
Introduce sysfs attributes to get the different level processor
frequencies.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit ec4e3326a95507ea96fbad21b9472f5ba25500a7)
Signed-off-by: You-Sheng Yang <vicamo.yang@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>