vmdevices: move devices type into hwclass module

This patch moves the device types in a new
'hwclass' module, and renames the various vm.${NAME}_DEVICES
into the corresponding hwclass.${NAME}
with no changes in behaviour.

This patch, has little value on its own, but is
needed to move away more code from vm into vmdevices.

Change-Id: Id7a3bdb3cb2269e85e83d8c688582e61473f688f
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34556
Reviewed-by: Dan Kenigsberg <danken@redhat.com>