libxl: support soundhw for hvm domains
libxl: support soundhw for hvm domains

The xend driver and the parsing/formating code in src/xenconfig
have long supported soundhw.  Add support in the libxl driver too.

libvirt/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,taget/libvirt,agx/libvirt,crobinso/libvirt,zippy2/libvirt,jardasgit/libvirt,andreabolognani/libvirt,eskultety/libvirt,rlaager/libvirt,crobinso/libvirt,datto/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,jfehlig/libvirt,nertpinx/libvirt,crobinso/libvirt,rlaager/libvirt,taget/libvirt,andreabolognani/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,VenkatDatta/libvirt,olafhering/libvirt,fabianfreyer/libvirt,eskultety/libvirt,datto/libvirt,zippy2/libvirt,VenkatDatta/libvirt,libvirt/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,olafhering/libvirt,taget/libvirt,agx/libvirt,zippy2/libvirt,olafhering/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,taget/libvirt,libvirt/libvirt,andreabolognani/libvirt,agx/libvirt,nertpinx/libvirt,zippy2/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,rlaager/libvirt,crobinso/libvirt,jfehlig/libvirt,datto/libvirt,taget/libvirt,rlaager/libvirt,fabianfreyer/libvirt,agx/libvirt,nertpinx/libvirt,jardasgit/libvirt,eskultety/libvirt,agx/libvirt,nertpinx/libvirt,rlaager/libvirt,eskultety/libvirt,datto/libvirt,eskultety/libvirt,jardasgit/libvirt,datto/libvirt,olafhering/libvirt,nertpinx/libvirt