ASoC: fsl ssi doc: Move optional properties to the correct section

Properties 'fsl,ssi-asynchronous', 'fsl,playback-dma' and 'fsl,capture-dma'
are optional, so move them under the optional section of the document.

While at it mention that 'fsl,playback-dma' and 'fsl,capture-dma'
only apply to Power Architecture.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Timur Tabi <timur@tabi.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/fsl,ssi.txt

@@ -20,24 +20,8 @@ Required properties:
                     have.
 - interrupt-parent: The phandle for the interrupt controller that
                     services interrupts for this device.
-- fsl,playback-dma: Phandle to a node for the DMA channel to use for
-                    playback of audio.  This is typically dictated by SOC
-                    design.  See the notes below.
-- fsl,capture-dma:  Phandle to a node for the DMA channel to use for
-                    capture (recording) of audio.  This is typically dictated
-                    by SOC design.  See the notes below.
 - fsl,fifo-depth:   The number of elements in the transmit and receive FIFOs.
                     This number is the maximum allowed value for SFCSR[TFWM0].
-- fsl,ssi-asynchronous:
-                    If specified, the SSI is to be programmed in asynchronous
-                    mode.  In this mode, pins SRCK, STCK, SRFS, and STFS must
-                    all be connected to valid signals.  In synchronous mode,
-                    SRCK and SRFS are ignored.  Asynchronous mode allows
-                    playback and capture to use different sample sizes and
-                    sample rates.  Some drivers may require that SRCK and STCK
-                    be connected together, and SRFS and STFS be connected
-                    together.  This would still allow different sample sizes,
-                    but not different sample rates.
  - clocks:          "ipg" - Required clock for the SSI unit
                     "baud" - Required clock for SSI master mode. Otherwise this
 		      clock is not used
@@ -61,6 +45,24 @@ Optional properties:
 - fsl,mode:         The operating mode for the AC97 interface only.
                     "ac97-slave" - AC97 mode, SSI is clock slave
                     "ac97-master" - AC97 mode, SSI is clock master
+- fsl,ssi-asynchronous:
+                    If specified, the SSI is to be programmed in asynchronous
+                    mode.  In this mode, pins SRCK, STCK, SRFS, and STFS must
+                    all be connected to valid signals.  In synchronous mode,
+                    SRCK and SRFS are ignored.  Asynchronous mode allows
+                    playback and capture to use different sample sizes and
+                    sample rates.  Some drivers may require that SRCK and STCK
+                    be connected together, and SRFS and STFS be connected
+                    together.  This would still allow different sample sizes,
+                    but not different sample rates.
+- fsl,playback-dma: Phandle to a node for the DMA channel to use for
+                    playback of audio.  This is typically dictated by SOC
+                    design.  See the notes below.
+                    Only used on Power Architecture.
+- fsl,capture-dma:  Phandle to a node for the DMA channel to use for
+                    capture (recording) of audio.  This is typically dictated
+                    by SOC design.  See the notes below.
+                    Only used on Power Architecture.
 
 Child 'codec' node required properties:
 - compatible:       Compatible list, contains the name of the codec