docs: cgroup-v1: convert docs to ReST and rename to *.rst

Convert the cgroup-v1 files to ReST format, in order to
allow a later addition to the admin-guide.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/scheduler/sched-deadline.txt

@@ -652,7 +652,7 @@ CONTENTS
 
  -deadline tasks cannot have an affinity mask smaller that the entire
  root_domain they are created on. However, affinities can be specified
- through the cpuset facility (Documentation/cgroup-v1/cpusets.txt).
+ through the cpuset facility (Documentation/cgroup-v1/cpusets.rst).
 
 5.1 SCHED_DEADLINE and cpusets HOWTO
 ------------------------------------

Documentation/scheduler/sched-design-CFS.txt

@@ -215,7 +215,7 @@ SCHED_BATCH) tasks.
 
    These options need CONFIG_CGROUPS to be defined, and let the administrator
    create arbitrary groups of tasks, using the "cgroup" pseudo filesystem.  See
-   Documentation/cgroup-v1/cgroups.txt for more information about this filesystem.
+   Documentation/cgroup-v1/cgroups.rst for more information about this filesystem.
 
 When CONFIG_FAIR_GROUP_SCHED is defined, a "cpu.shares" file is created for each
 group created using the pseudo filesystem.  See example steps below to create

Documentation/scheduler/sched-rt-group.txt

@@ -133,7 +133,7 @@ This uses the cgroup virtual file system and "<cgroup>/cpu.rt_runtime_us"
 to control the CPU time reserved for each control group.
 
 For more information on working with control groups, you should read
-Documentation/cgroup-v1/cgroups.txt as well.
+Documentation/cgroup-v1/cgroups.rst as well.
 
 Group settings are checked against the following limits in order to keep the
 configuration schedulable: