riscv: dts: starfive: Prevent binman from relocating symbols in SPL

SPL and proper U-Boot are split into two images with default binman
configuration of StarFive VisionFive 2, thus proper U-Boot symbols
cannot be found in the SPL image. This fixes errors like

  Section '/binman/spl-img': Symbol '_binman_u_boot_any_prop_size'
    in entry '/binman/spl-img/mkimage/u-boot-spl/u-boot-spl-nodtb':
      Entry 'u-boot-any' not found in list (u-boot-spl-nodtb,
      u-boot-spl-dtb,u-boot-spl,mkimage,spl-img)

Fixes: 90602e779d3 ("riscv: dts: starfive: generate u-boot-spl.bin.normal.out")
Suggested-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Yao Zi <ziyao@disroot.org>

arch/riscv/dts/starfive-visionfive2-binman.dtsi

@@ -20,6 +20,7 @@
 			args = "-T sfspl";
 
 			u-boot-spl {
+				no-write-symbols;
 			};
 		};
 	};