mfd: Improve mc13xxx dt binding document

It improves mc13xxx dt binding document on how the regulator name
is being used for binding a mc13892 regulator device.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

Documentation/devicetree/bindings/mfd/mc13xxx.txt

@@ -10,9 +10,34 @@ Optional properties:
 - fsl,mc13xxx-uses-touch : Indicate the touchscreen controller is being used
 
 Sub-nodes:
-- regulators : Contain the regulator nodes.  The name of regulator node
-  is being used by mc13xxx regulator driver to find the correct relator
-  device.
+- regulators : Contain the regulator nodes.  The MC13892 regulators are
+  bound using their names as listed below with their registers and bits
+  for enabling.
+
+    vcoincell : regulator VCOINCELL (register 13, bit 23)
+    sw1       : regulator SW1	    (register 24, bit 0)
+    sw2       : regulator SW2	    (register 25, bit 0)
+    sw3       : regulator SW3	    (register 26, bit 0)
+    sw4       : regulator SW4	    (register 27, bit 0)
+    swbst     : regulator SWBST	    (register 29, bit 20)
+    vgen1     : regulator VGEN1	    (register 32, bit 0)
+    viohi     : regulator VIOHI	    (register 32, bit 3)
+    vdig      : regulator VDIG	    (register 32, bit 9)
+    vgen2     : regulator VGEN2	    (register 32, bit 12)
+    vpll      : regulator VPLL	    (register 32, bit 15)
+    vusb2     : regulator VUSB2	    (register 32, bit 18)
+    vgen3     : regulator VGEN3	    (register 33, bit 0)
+    vcam      : regulator VCAM	    (register 33, bit 6)
+    vvideo    : regulator VVIDEO    (register 33, bit 12)
+    vaudio    : regulator VAUDIO    (register 33, bit 15)
+    vsd       : regulator VSD	    (register 33, bit 18)
+    gpo1      : regulator GPO1	    (register 34, bit 6)
+    gpo2      : regulator GPO2	    (register 34, bit 8)
+    gpo3      : regulator GPO3	    (register 34, bit 10)
+    gpo4      : regulator GPO4	    (register 34, bit 12)
+    pwgt1spi  : regulator PWGT1SPI  (register 34, bit 15)
+    pwgt2spi  : regulator PWGT2SPI  (register 34, bit 16)
+    vusb      : regulator VUSB	    (register 50, bit 3)
 
   The bindings details of individual regulator device can be found in:
   Documentation/devicetree/bindings/regulator/regulator.txt