of: dynamic: restrict overlay by targets

Restrict which nodes are valid targets for a DT overlay.

Add a flag bit to struct device_node allowing nodes to be marked as valid target for overlays.

A driver that is always intended to handle DT overlays can enable overlays by calling a function for its DT node.

For individual nodes that need to be opened up for a specific use, adding the property "overlay-allowed" enables overlays targeting that node. I'll need to document the DT property, not sure where specifically. New file bindings/overlay.txt?

This patchset differs from the RFC:
* Added a flag bit and got rid of the whitelist
* Renamed the functions that enable a node
* Added a DT property

Alan Tull (2):
of: overlay: add flag enabling overlays and enable fpga-region
overlays
of: dynamic: add overlay-allowed DT property

 drivers/fpga/of-fpga-region.c |  4 ++++
 drivers/of/base.c             |  4 ++--
 drivers/of/dynamic.c          |  3 +++
 drivers/of/fdt.c              |  3 +++
 drivers/of/of_private.h       |  2 ++
 drivers/of/overlay.c          | 26 ++++++++++++++++++++++++++
 include/linux/of.h            | 19 +++++++++++++++++++
 7 files changed, 59 insertions(+), 2 deletions(-)

2.7.4