conf: Rework virDomainDeviceDefPostParseCommon()
conf: Rework virDomainDeviceDefPostParseCommon()

Now that we've moved all the actual code into helper
functions, we can turn it into a switch statement.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

andreabolognani/libvirt,eskultety/libvirt,olafhering/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,eskultety/libvirt,crobinso/libvirt,olafhering/libvirt,nertpinx/libvirt,jfehlig/libvirt,libvirt/libvirt,eskultety/libvirt,jfehlig/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,eskultety/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,zippy2/libvirt,crobinso/libvirt,jardasgit/libvirt,zippy2/libvirt,libvirt/libvirt,libvirt/libvirt,andreabolognani/libvirt,nertpinx/libvirt,andreabolognani/libvirt,jardasgit/libvirt,zippy2/libvirt,eskultety/libvirt,jfehlig/libvirt,jardasgit/libvirt,olafhering/libvirt,libvirt/libvirt,jardasgit/libvirt,crobinso/libvirt,olafhering/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt