cpufreq/amd-pstate: Only print supported EPP values for performance governor

show_energy_performance_available_preferences() to show only supported
values which is performance in performance governor policy.

-------Before--------
$ cat /sys/devices/system/cpu/cpu1/cpufreq/scaling_driver
amd-pstate-epp
$ cat /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
performance
$ cat /sys/devices/system/cpu/cpu1/cpufreq/energy_performance_preference
performance
$ cat /sys/devices/system/cpu/cpu1/cpufreq/energy_performance_available_preferences
default performance balance_performance balance_power power

-------After--------
$ cat /sys/devices/system/cpu/cpu1/cpufreq/scaling_driver
amd-pstate-epp
$ cat /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
performance
$ cat /sys/devices/system/cpu/cpu1/cpufreq/energy_performance_preference
performance
$ cat /sys/devices/system/cpu/cpu1/cpufreq/energy_performance_available_preferences
performance

Fixes: ffa5096a ("cpufreq: amd-pstate: implement Pstate EPP su...