riscv: Add S-mode defconfigs for QEMU virt machine

This patch adds S-mode defconfigs for QEMU virt machine so
that we can run u-boot in S-mode on QEMU using M-mode runtime
firmware (BBL or equivalent).

Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
diff --git a/configs/qemu-riscv64_smode_defconfig b/configs/qemu-riscv64_smode_defconfig
new file mode 100644
index 0000000..b012443
--- /dev/null
+++ b/configs/qemu-riscv64_smode_defconfig
@@ -0,0 +1,11 @@
+CONFIG_RISCV=y
+CONFIG_TARGET_QEMU_VIRT=y
+CONFIG_ARCH_RV64I=y
+CONFIG_RISCV_SMODE=y
+CONFIG_DISTRO_DEFAULTS=y
+CONFIG_NR_DRAM_BANKS=1
+CONFIG_FIT=y
+CONFIG_DISPLAY_CPUINFO=y
+CONFIG_DISPLAY_BOARDINFO=y
+# CONFIG_CMD_MII is not set
+CONFIG_OF_PRIOR_STAGE=y