perf: add cpu_clock software perf event support

This patch adds support and documentation for
the cpu_clock perf event.

Signed-off-by: Nitesh Konkar <nitkon12@linux.vnet.ibm.com>

docs/formatdomain.html.in

@@ -1947,6 +1947,7 @@
   <event name='stalled_cycles_frontend' enabled='no'/>
   <event name='stalled_cycles_backend' enabled='no'/>
   <event name='ref_cpu_cycles' enabled='no'/>
+  <event name='cpu_clock' enabled='no'/>
 </perf>
 ...
 </pre>
@@ -2025,6 +2026,13 @@
          by applications running on the platform</td>
       <td><code>perf.ref_cpu_cycles</code></td>
     </tr>
+    <tr>
+      <td><code>cpu_clock</code></td>
+      <td>the count of cpu clock time, as measured by a monotonic
+          high-resolution per-CPU timer, by applications running on
+          the platform</td>
+      <td><code>perf.cpu_clock</code></td>
+    </tr>
   </table>
 
     <h3><a name="elementsDevices">Devices</a></h3>

docs/schemas/domaincommon.rng

@@ -433,6 +433,7 @@
               <value>stalled_cycles_frontend</value>
               <value>stalled_cycles_backend</value>
               <value>ref_cpu_cycles</value>
+              <value>cpu_clock</value>
             </choice>
           </attribute>
           <attribute name="enabled">