riscv: enable CONFIG_CMD_SBI for QEMU boards

Let CONFIG_TARGET_QEMU_VIRT imply CONFIG_CMD_SBI.

The sbi command provides detailed information about the SBI.
It is useful to test the discovery of extensions.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/board/emulation/qemu-riscv/Kconfig b/board/emulation/qemu-riscv/Kconfig
index 02bf847..d8c57e6 100644
--- a/board/emulation/qemu-riscv/Kconfig
+++ b/board/emulation/qemu-riscv/Kconfig
@@ -37,6 +37,7 @@
 	imply SPL_RAM_DEVICE
 	imply CMD_PCI
 	imply CMD_POWEROFF
+	imply CMD_SBI
 	imply CMD_SCSI
 	imply CMD_PING
 	imply CMD_EXT2