Implement new QB_DRIVE_TYPE="/dev/vdb" which falls back
to virtio block device emulated by qemu.
That is needed to support following qemu command line:
-drive id=disk0,file=%s,if=none,format=%s \
-device virtio-blk-device,drive=disk0'
Real use case is arm64 emulation with qemu with atf+optee+uboot,
so that uboot driver sees this disk and able to load from it.
Signed-off-by: Maxim Uvarov <maxim.uvarov@linaro.org> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
