dt-bindings: mtd: oxnas-nand: remove obsolete bindings

Due to lack of maintenance and stall of development for a few years now,
and since no new features will ever be added upstream, remove the
for OX810 and OX820 nand bindings.
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230630-topic-oxnas-upstream-remove-v2-6-fb6ab3dea87c@linaro.org

Documentation/devicetree/bindings/mtd/oxnas-nand.txt

-* Oxford Semiconductor OXNAS NAND Controller
-
-Please refer to nand-controller.yaml for generic information regarding MTD NAND bindings.
-
-Required properties:
- - compatible: "oxsemi,ox820-nand"
- - reg: Base address and length for NAND mapped memory.
-
-Optional Properties:
- - clocks: phandle to the NAND gate clock if needed.
- - resets: phandle to the NAND reset control if needed.
-
-Example:
-
-nandc: nand-controller@41000000 {
-	compatible = "oxsemi,ox820-nand";
-	reg = <0x41000000 0x100000>;
-	clocks = <&stdclk CLK_820_NAND>;
-	resets = <&reset RESET_NAND>;
-	#address-cells = <1>;
-	#size-cells = <0>;
-
-	nand@0 {
-		reg = <0>;
-		#address-cells = <1>;
-		#size-cells = <1>;
-		nand-ecc-mode = "soft";
-		nand-ecc-algo = "hamming";
-
-		partition@0 {
-			label = "boot";
-			reg = <0x00000000 0x00e00000>;
-			read-only;
-		};
-
-		partition@e00000 {
-			label = "ubi";
-			reg = <0x00e00000 0x07200000>;
-		};
-	};
-};