dmaengine: doc: Add ReST style dmaengine document

This removes the index file and adds the index.rst as placeholder
and update driver-api index to add dmaengine. As a consequence
dmaengine documentation will be in driver-api/
Signed-off-by: NVinod Koul <vinod.koul@intel.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/dmaengine/00-INDEX

-00-INDEX
-	- this file.
-client.txt
-	-the DMA Engine API Guide.
-dmatest.txt
-	- how to compile, configure and use the dmatest system.
-provider.txt
-	- the DMA controller API.
\ No newline at end of file

Documentation/driver-api/dmaengine/index.rst

+=======================
+DMAEngine documentation
+=======================
+
+DMAEngine documentation provides documents for various aspects of DMAEngine
+framework.
+
+.. only::  subproject
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/index.rst

@@ -46,6 +46,7 @@ available subsections can be seen below.
    pinctl
    gpio
    misc_devices
+   dmaengine/index
 
 .. only::  subproject and html