riscv: dts: binman.dtsi: Switch to u-boot-nodtb entry for proper U-Boot

riscv: dts: binman.dtsi: Switch to u-boot-nodtb entry for proper U-Boot

Switch to u-boot-nodtb entry which precisely represents a proper U-Boot
and could be matched with u_boot_any. This allows RISC-V ports that make
use of binman to be built without disabling SPL_BINMAN_UBOOT_SYMBOLS
explicitly, which is set to y by default.

Fixes: 0784510f741 ("riscv: sifive: unleashed: Switch to use binman to generate u-boot.itb")
Suggested-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Yao Zi <ziyao@disroot.org>
Reviewed-by: Simon Glass <sjg@chromium.org>