release: make dependencies, not recursive make

For historical reasons, the vm-release and cloudware-release targets
were written as recursive makes of ${VMTARGETS} and ${CLOUDTARGETS};
this worked fine until we started running make release -jN and
had both VM and cloud targets depending on ${QEMUTGT}, at which
point things exploded when we tried to build the port twice at the
same time.

Switch vm-release and cloudware-release to have make dependencies on
their individual components; this way a single make process runs and
is aware of the duplicate dependency (and only runs it once).

MFC after: 5 days

(cherry picked from commit ce7756fdca1f0a89a74bc406cd3d3ac1d1be1ffb)