Documentation: add devicetree docs index file

The device tree infrastructure is being genericized so its documentation
moved out of the PowerPC directory.

Signed-off-by: Rob Landley <rlandley@parallels.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/devicetree/00-INDEX

@@ -0,0 +1,10 @@
+Documentation for device trees, a data structure by which bootloaders pass
+hardware layout to Linux in a device-independent manner, simplifying hardware
+probing.  This subsystem is maintained by Grant Likely
+<grant.likely@secretlab.ca> and has a mailing list at
+https://lists.ozlabs.org/listinfo/devicetree-discuss
+
+00-INDEX
+	- this file
+booting-without-of.txt
+	- Booting Linux without Open Firmware, describes history and format of device trees.

Documentation/powerpc/00-INDEX

@@ -5,8 +5,6 @@ please mail me.
 
 00-INDEX
 	- this file
-booting-without-of.txt
-	- Booting the Linux/ppc kernel without Open Firmware
 cpu_features.txt
 	- info on how we support a variety of CPUs with minimal compile-time
 	options.
@@ -16,8 +14,6 @@ hvcs.txt
 	- IBM "Hypervisor Virtual Console Server" Installation Guide
 mpc52xx.txt
 	- Linux 2.6.x on MPC52xx family
-mpc52xx-device-tree-bindings.txt
-	- MPC5200 Device Tree Bindings
 sound.txt
 	- info on sound support under Linux/PPC
 zImage_layout.txt