powerpc: vio: move device attributes into a new ifdef

In order to make the distinction of the vio_bus_type variable based on
CONFIG_PPC_SMLPAR more explicit, move the required structs into a new
ifdef block. This is needed in order to make vio_bus_type const and
because the distinction is made explicit, there is no need to set the
fields within the vio_cmo_sysfs_init function.

Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240212-bus_cleanup-powerpc2-v2-1-8441b3f77827@marliere.net