riscv: Build loader.bin exclusively for Canaan K210

According to the explanation in commit ef10bdf ("riscv:
Kconfig.socs: Split ARCH_CANAAN and SOC_CANAAN_K210"),
loader.bin is a special feature of the Canaan K210 and
is not applicable to other SoCs.

Fixes: e79dfcb ("riscv: make image compression configurable")
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Link: https://lore.kernel.org/r/20251029094429.553842-1-jiangfeng@kylinos.cn
Signed-off-by: Paul Walmsley <pjw@kernel.org>

Author: flynnjiang

arch/riscv/Makefile

@@ -159,7 +159,7 @@ boot-image-$(CONFIG_KERNEL_LZO)		:= Image.lzo
 boot-image-$(CONFIG_KERNEL_ZSTD)	:= Image.zst
 boot-image-$(CONFIG_KERNEL_XZ)		:= Image.xz
 ifdef CONFIG_RISCV_M_MODE
-boot-image-$(CONFIG_ARCH_CANAAN)	:= loader.bin
+boot-image-$(CONFIG_SOC_CANAAN_K210)	:= loader.bin
 endif
 boot-image-$(CONFIG_EFI_ZBOOT)		:= vmlinuz.efi
 boot-image-$(CONFIG_XIP_KERNEL)		:= xipImage