riscv: dts: add SiFive Unmatched board support

Add dts files for SiFive Unmatched board.

Signed-off-by: Green Wan <green.wan@sifive.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/arch/riscv/dts/Makefile b/arch/riscv/dts/Makefile
index 26ef853..7778874 100644
--- a/arch/riscv/dts/Makefile
+++ b/arch/riscv/dts/Makefile
@@ -4,6 +4,7 @@
 dtb-$(CONFIG_TARGET_MICROCHIP_ICICLE) += microchip-mpfs-icicle-kit.dtb
 dtb-$(CONFIG_TARGET_QEMU_VIRT) += qemu-virt.dtb
 dtb-$(CONFIG_TARGET_SIFIVE_UNLEASHED) += hifive-unleashed-a00.dtb
+dtb-$(CONFIG_TARGET_SIFIVE_UNMATCHED) += hifive-unmatched-a00.dtb
 dtb-$(CONFIG_TARGET_SIPEED_MAIX) += k210-maix-bit.dtb
 
 targets += $(dtb-y)