OF: DT-Overlay configfs interface (v8)

commit 7e42c87c489b702795794e480fb5483897ff9e91 from
https://github.com/Xilinx/linux-xlnx.git



Add a runtime interface to using configfs for generic device tree overlay
usage. With it its possible to use device tree overlays without having
to use a per-platform overlay manager.

Please see Documentation/devicetree/configfs-overlays.txt for more info.

Changes since v7:
- Xilinx alignment
- of: configfs: Fix error handling from of_overlay_create()
- of: configfs: lock while resolving and applying
- of: configfs: Fix memory leak in create overlay
- of: configfs: Fix compilation warning
- of: configfs: Use of_overlay_fdt_apply API call

Changes since v6:
- Default groups properties API changed.

Changes since v5:
- New style configfs.

Changes since v4:
- Loading fix for multiple overlays as found out by
  Geert Uytterhoeven <geert@linux-m68k.org>

Changes since v3:
- Fixed compilation on SPARC & Xtensa

Changes since v2:
- Removed ifdef CONFIG_OF_OVERLAY (since for now it's required)
- Created a documentation entry
- Slight rewording in Kconfig

Changes since v1:
- of_resolve() -> of_resolve_phandles().

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
State: not-upstreamable
[michals: Squashed with
OF: overlay: Perform RCU callback barrier before releasing overlay memory resources
]
Signed-off-by: Liwei Song <liwei.song@windriver.com>