rapidio: move net allocation into core code

Make net allocation/release routines available to all components of
RapidIO subsystem by moving code from rio-scan enumerator.

Make destination ID allocation method private to existing enumerator
because other enumeration methods can use their own algorithm.

Setup net device object as a parent of all RapidIO devices residing in
it and register net as a child of active mport device.

Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: Andre van Herk <andre.van.herk@prodrive-technologies.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>