qemu-helper: depend on unfs3 and pseudo directly

The eliminates having to do extra steps (e.g. meta-ide-support)
when booting an image with a nfs mount as rootfs - startng runqemu
with a nfs mount starts to 'just work' after building an image.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>