qemu: add to host utilities menu

This allows qemu-user to be selected by the user. One use case
for this is to call qemu-user from post build scripts to
run regression tests against the build.

Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>