qemu_process: Deduplicate code in qemuProcessNeedHugepagesPath()

qemu_process: Deduplicate code in qemuProcessNeedHugepagesPath()

The aim of qemuProcessNeedHugepagesPath() is to return whether
guest needs private path inside HugeTLBFS mounts (deducted from
domain definition @def) or whether the memory device that user is
hotplugging in needs the private path (deducted from the @mem
argument). The actual creation of the path is done in the only
caller qemuProcessBuildDestroyMemoryPaths().

The rule for the first case (@def) and the second case (@mem) is
the same (domain has a DIMM device that has HP requested) and is
written twice. Move the logic into a function to deduplicate the
code.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>