Rename struct channel_path_desc to struct channel_path_desc_fmt0
to fit the scheme. Provide a macro for the function wrappers that
gather this and related data from firmware.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>