migration/multifd: Register nocomp ops dynamically

migration/multifd: Register nocomp ops dynamically

Prior to moving the ram code into multifd-nocomp.c, change the code to
register the nocomp ops dynamically so we don't need to have the ops
structure defined in multifd.c.

While here, move the ops struct initialization to the end of the file
to make the next diff cleaner.

Reviewed-by: Prasad Pandit <pjp@fedoraproject.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>