Update enumeration/discovery method registration mechanism to allow
loading enumeration/discovery methods before all mports are registered.

Existing statically linked RapidIO subsystem expects that all available
RapidIO mport devices are initialized and registered before the
enumeration/discovery method is registered.  Switching to loadable mport
device drivers creates situation when mport device driver can be loaded
after enumeration/discovery method is attached (e.g., loadable mport
driver in a system with statically linked RapidIO core and enumerator).
This also will happen in a system with hot-pluggable RapidIO controllers.

To remove the dependency on the initialization/registration order this
patch introduces enumeration/discovery registration mechanism that
supports arbitrary registration order of mports and enumerator/discovery
methods.

The following registration rules are implemented:
- only one enumeration/discovery method can be registered for given mport ID
  (including RIO_MPORT_ANY);
- when new enumeration/discovery methods tries to attach to the registered mport
  device, method with matching mport ID will replace a default method previously
  registered for given mport (if any);
- enumeration/discovery method with target ID=RIO_MPORT_ANY will be attached
  only to mports that do not have another enumerator attached to them;
- when new mport device is registered with RapidIO subsystem, registration
  routine searches for the enumeration/discovery method with the best matching
  mport ID;
Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Li Yang <leoli@freescale.com>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: Andre van Herk <andre.van.herk@Prodrive.nl>
Cc: Micha Nelissen <micha.nelissen@Prodrive.nl>
Cc: Stef van Os <stef.van.os@Prodrive.nl>
Cc: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>