scripts: Cover sifive/fu540 in the 32-bit build

We now support building sifive/fu540 as a 32-bit platform. Add it
in the 32-bit platform list of binary archive script.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>

scripts/create-binary-archive.sh

@@ -85,6 +85,7 @@ case "${BUILD_RISCV_XLEN}" in
 32)
 	# Setup 32-bit platform list
 	BUILD_PLATFORM_SUBDIR=("qemu/virt")
+	BUILD_PLATFORM_SUBDIR+=("sifive/fu540")
 	;;
 64)
 	# Setup 64-bit platform list