docs: dt: fix several broken doc references

There are several DT doc references that require manual fixes.
I found 3 cases fixed on this patch:

- directory named "binding/" instead of "bindings/";
- .txt to .yaml renames;
- file renames (still on txt format);

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

dt-bindings: mtd: Add Cadence NAND controller driver

Document the bindings used by Cadence NAND controller driver

Signed-off-by: Piotr Sroka <piotrs@cadence.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>