regmap: Add explict native endian flag to DT bindings

Currently the binding document says that if no endianness is configured
we use native endian but this is not in fact true for all binding types
and we do have some devices that really want native endianness such as
Broadcom MIPS SoCs where switching the endianness of the CPU also
switches the endianness of external IPs.

Provide an explicit option for this.
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regmap/regmap.txt

@@ -5,15 +5,18 @@ Index     Device     Endianness properties
 ---------------------------------------------------
 1         BE         'big-endian'
 2         LE         'little-endian'
+3	  Native     'native-endian'
 
 For one device driver, which will run in different scenarios above
 on different SoCs using the devicetree, we need one way to simplify
 this.
 
-Required properties:
-- {big,little}-endian: these are boolean properties, if absent
-  meaning that the CPU and the Device are in the same endianness mode,
-  these properties are for register values and all the buffers only.
+Optional properties:
+- {big,little,native}-endian: these are boolean properties, if absent
+  then the implementation will choose a default based on the device
+  being controlled.  These properties are for register values and all
+  the buffers only.  Native endian means that the CPU and device have
+  the same endianness.
 
 Examples:
 Scenario 1 : CPU in LE mode & device in LE mode.

drivers/base/regmap/regmap.c

@@ -557,6 +557,8 @@ enum regmap_endian regmap_get_val_endian(struct device *dev,
 			endian = REGMAP_ENDIAN_BIG;
 		else if (of_property_read_bool(np, "little-endian"))
 			endian = REGMAP_ENDIAN_LITTLE;
+		else if (of_property_read_bool(np, "native-endian"))
+			endian = REGMAP_ENDIAN_NATIVE;
 
 		/* If the endianness was specified in DT, use that */
 		if (endian != REGMAP_ENDIAN_DEFAULT)