cpufreq: amd-pstate: Remove fast_switch_possible flag from active driver

amd_pstate active mode driver is only compatible with static governors.
Therefore it doesn't need fast_switch functionality. Remove
fast_switch_possible flag from amd_pstate active mode driver.

Fixes: ffa5096a ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
Signed-off-by: Wyes Karny <wyes.karny@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>