docs: cpu-freq: convert index.txt to ReST

most of the stuff there can be re-used with ReST format,
but we need to add an empty TOC and remove the existing
entries, as the following conversion patches will be re-adding
them, as they're converted.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/cpu-freq/index.txt → Documentation/cpu-freq/index.rst

-     CPU frequency and voltage scaling code in the Linux(TM) kernel
-
-
-		         L i n u x    C P U F r e q
-
-
-
-
-		    Dominik Brodowski  <linux@brodo.de>
+.. SPDX-License-Identifier: GPL-2.0
 
+==============================================================================
+Linux CPUFreq - CPU frequency and voltage scaling code in the Linux(TM) kernel
+==============================================================================
 
+Author: Dominik Brodowski  <linux@brodo.de>
 
    Clock scaling allows you to change the clock speed of the CPUs on the
    fly. This is a nice method to save battery power, because the lower
    the clock speed, the less power the CPU consumes.
 
 
-
-Documents in this directory:
-----------------------------
-
-amd-powernow.txt -	AMD powernow driver specific file.
-
-core.txt	-	General description of the CPUFreq core and
-			of CPUFreq notifiers.
-
-cpu-drivers.txt -	How to implement a new cpufreq processor driver.
-
-cpufreq-nforce2.txt -	nVidia nForce2 platform specific file.
-
-cpufreq-stats.txt -	General description of sysfs cpufreq stats.
-
-index.txt	-	File index, Mailing list and Links (this document)
-
-pcc-cpufreq.txt -	PCC cpufreq driver specific file.
-
+.. toctree::
+   :maxdepth: 1
 
 Mailing List
 ------------

Documentation/index.rst

@@ -99,6 +99,7 @@ needed).
    accounting/index
    block/index
    cdrom/index
+   cpu-freq/index
    ide/index
    fb/index
    fpga/index