dt-bindings: remove 'interrupt-parent' from bindings

'interrupt-parent' is often documented as part of define bindings, but
it is really outside the scope of a device binding. It's never required
in a given node as it is often inherited from a parent node. Or it can
be implicit if a parent node is an 'interrupt-controller' node. So
remove it from all the binding files.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

dt: binding: reword PowerPC 8xxx GPIO documentation

re-format and re-word the device tree binding documentation for MPC8xxx
and compatibles, reference the common document for interrupt controllers
and remove outdated duplicate SoC specific information

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <Pawel.Moll@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: <devicetree@vger.kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>

dt: Move device tree documentation out of powerpc directory

The device tree is used by more than just PowerPC. Make the documentation
directory available to all.

v2: reorganized files while moving to create arch and driver specific
directories.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>