riscv: qemu: Split devicetree files for qemu_riscv32/64

This uses QEMU virt which creates its own devicetree.

Copy the existing empty version of this file, so splitting the existing
qemu-virt into two, since anyone actually trying to use this will need a
different devicetree for 32- and 64-bit machines.

Tested-by: Heinrich Schuchardt <heinrich.schuchardt@canaonical.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/riscv/dts/Makefile b/arch/riscv/dts/Makefile
index b6e9166..90d3f35 100644
--- a/arch/riscv/dts/Makefile
+++ b/arch/riscv/dts/Makefile
@@ -2,7 +2,7 @@
 
 dtb-$(CONFIG_TARGET_AX25_AE350) += ae350_32.dtb ae350_64.dtb
 dtb-$(CONFIG_TARGET_MICROCHIP_ICICLE) += microchip-mpfs-icicle-kit.dtb
-dtb-$(CONFIG_TARGET_QEMU_VIRT) += qemu-virt.dtb
+dtb-$(CONFIG_TARGET_QEMU_VIRT) += qemu-virt32.dtb qemu-virt64.dtb
 dtb-$(CONFIG_TARGET_OPENPITON_RISCV64) += openpiton-riscv64.dtb
 dtb-$(CONFIG_TARGET_SIFIVE_UNLEASHED) += hifive-unleashed-a00.dtb
 dtb-$(CONFIG_TARGET_SIFIVE_UNMATCHED) += hifive-unmatched-a00.dtb