intel_pstate: Update documentation of {max,min}_perf_pct sysfs files

Update documentation to make the interpretation of the values clearer

Link: https://bugzilla.kernel.org/show_bug.cgi?id=64251
Cc: 3.13+ <[e-mail]> # 3.13+
Signed-off-by: Dirk Brandewie <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/cpu-freq/intel-pstate.txt

···
 /sys/devices/system/cpu/intel_pstate/
 
       max_perf_pct: limits the maximum P state that will be requested by
-      the driver stated as a percentage of the available performance.
+      the driver stated as a percentage of the available performance. The
+      available (P states) performance may be reduced by the no_turbo
+      setting described below.
 
       min_perf_pct: limits the minimum P state that will be  requested by
-      the driver stated as a percentage of the available performance.
+      the driver stated as a percentage of the max (non-turbo)
+      performance level.
 
       no_turbo: limits the driver to selecting P states below the turbo
       frequency range.