docs: hwmon: add RAA228244 and RAA228246 info to isl68137 documentation

The Renesas RAA228244 and RAA228246 are recently released digital
multiphase controllers.

Signed-off-by: Grant Peltier <[e-mail]>
Link: https://lore.kernel.org/r/ddeaf4[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

Documentation/hwmon/isl68137.rst

···
 
       Publicly available (after August 2020 launch) at the Renesas website
 
+  * Renesas RAA228244
+
+    Prefix: 'raa228244'
+
+    Addresses scanned: -
+
+    Datasheet:
+
+      Provided by Renesas upon request and NDA
+
+  * Renesas RAA228246
+
+    Prefix: 'raa228246'
+
+    Addresses scanned: -
+
+    Datasheet:
+
+      Provided by Renesas upon request and NDA
+
   * Renesas RAA229001
 
     Prefix: 'raa229001'