cpufreq: amd-pstate: Make amd-pstate EPP driver name hyphenated

cpufreq: amd-pstate: Make amd-pstate EPP driver name hyphenated

amd-pstate passive mode driver is hyphenated. So make amd-pstate active
mode driver consistent with that rename "amd_pstate_epp" to
"amd-pstate-epp".

Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
Cc: All applicable <stable@vger.kernel.org>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Signed-off-by: Wyes Karny <wyes.karny@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>