rapidio/rionet: add locking into add/remove device

Add spinlock protection when handling list of connected peers and
ability to handle new peer device addition after the RIONET device was
open.  Before his update RIONET was sending JOIN requests only when it
have been opened, peer devices added later have been missing from this
process.

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>