riscv: qemu: Enable booting from NVMe

QEMU supports NVMe devices, but U-Boot only tries to boot from Virtio.
This is problematic when explicitly using NVMe, so fix that.

Additionally, RVVM virtual machine is almost fully compatible with QEMU,
except it only implements NVMe drives instead of VirtIO.
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

include/configs/qemu-riscv.h

@@ -22,6 +22,7 @@
 					"stderr=serial,vidconsole\0"
 
 #define BOOT_TARGET_DEVICES(func) \
+	func(NVME, nvme, 0) \
 	func(VIRTIO, virtio, 0) \
 	func(VIRTIO, virtio, 1) \
 	func(SCSI, scsi, 0) \