realtek: rename u-boot-env2 to board-name

Some realtek boards have two u-boot-env partitions. However, in the
DGS-1210 series, the mtdblock2 partition is not a valid u-boot env
and simply contains the board/device name, followed by nulls.

00000000  44 47 53 2d 31 32 31 30  2d 32 38 2d 46 31 00 00 |DGS-1210-28-F1..|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 |................|
*
00040000

00000000  44 47 53 2d 31 32 31 30  2d 35 32 2d 46 31 00 00 |DGS-1210-52-F1..|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 |................|
*
00040000

The misleading u-boot-env2 name also confuses uboot-envtools.
Signed-off-by: NLuiz Angelo Daros de Luca <luizluca@gmail.com>
(cherry picked from commit 8b798dbb)

target/linux/realtek/dts-5.10/rtl8382_d-link_dgs-1210.dtsi

@@ -55,7 +55,7 @@
 				read-only;
 			};
 			partition@c0000 {
-				label = "u-boot-env2";
+				label = "board-name";
 				reg = <0x000c0000 0x40000>;
 			};
 			partition@280000 {