ASoC: fsl: Mark 'big-endian' property as optional

Currently the 'big-endian' property is listed as required, which is
not correct. i.MX SoCs do not need such property, so move it under
'Optional properties' entry instead.

Also, fsl-sai.txt incorrectly referenced 'FTM_PWM registers', so
change it to 'SAI registers', which is the intended description.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

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

@@ -31,14 +31,16 @@ Required properties:
 			  it. This property is optional depending on the SoC
 			  design.
 
-   - big-endian		: If this property is absent, the little endian mode
-			  will be in use as default. Otherwise, the big endian
-			  mode will be in use for all the device registers.
-
    - fsl,asrc-rate	: Defines a mutual sample rate used by DPCM Back Ends.
 
    - fsl,asrc-width	: Defines a mutual sample width used by DPCM Back Ends.
 
+Optional properties:
+
+   - big-endian		: If this property is absent, the little endian mode
+			  will be in use as default. Otherwise, the big endian
+			  mode will be in use for all the device registers.
+
 Example:
 
 asrc: asrc@2034000 {

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

@@ -42,6 +42,8 @@ Required properties:
 			  means all the settings for Receiving would be
 			  duplicated from Transmition related registers.
 
+Optional properties:
+
   - big-endian		: If this property is absent, the native endian mode
 			  will be in use as default, or the big endian mode
 			  will be in use for all the device registers.

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

@@ -33,6 +33,8 @@ Required properties:
 			  it. This property is optional depending on the SoC
 			  design.
 
+Optional properties:
+
    - big-endian		: If this property is absent, the native endian mode
 			  will be in use as default, or the big endian mode
 			  will be in use for all the device registers.

Documentation/devicetree/bindings/sound/fsl-sai.txt

@@ -28,9 +28,6 @@ Required properties:
 			  pinctrl-names. See ../pinctrl/pinctrl-bindings.txt
 			  for details of the property values.
 
-  - big-endian		: Boolean property, required if all the FTM_PWM
-			  registers are big-endian rather than little-endian.
-
   - lsb-first		: Configures whether the LSB or the MSB is transmitted
 			  first for the fifo data. If this property is absent,
 			  the MSB is transmitted first as default, or the LSB
@@ -48,6 +45,11 @@ Required properties:
 			  receive data by following their own bit clocks and
 			  frame sync clocks separately.
 
+Optional properties:
+
+  - big-endian		: Boolean property, required if all the SAI
+			  registers are big-endian rather than little-endian.
+
 Optional properties (for mx6ul):
 
   - fsl,sai-mclk-direction-output: This is a boolean property. If present,