powerpc/85xx: Specify hwconfig usage for USB controller

Specify hwconfig usage for USB mode and phy change

Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

doc/README.fsl-hwconfig

@@ -19,3 +19,28 @@ audclk
 
 	'audclk:12'
 		Select the 12.288MHz clock
+
+usb
+	Specific to boards have USB controller
+
+	This option specifies the following for a USB controller:
+
+		- which controller mode to use
+		- which USB PHY to use
+
+	This is used by generic USB device-tree fixup function to update
+	modified values of phy type and controller mode.
+
+	Also used for configuring multiple USB controllers such that
+	'usbN' (where N is 1, 2, etc. refers to controller no.)
+
+	'phy_type'
+		Select USB phy type: 'utmi' OR 'ulpi'
+
+	'dr_mode'
+		Select USB controller mode: 'host', 'peripheral' OR 'otg'
+
+	Examples:
+		usb1:dr_mode=host;usb2:dr_mode=peripheral'
+
+		usb1:dr_mode=host,phy_type=utmi;usb2:dr_mode=host'