rapidio: add modular rapidio core build into powerpc and mips branches

Allow modular build option for RapidIO subsystem core in MIPS and PowerPC
architectural branches.

At this moment modular RapidIO subsystem build is enabled only for
platforms that use PCI/PCIe based RapidIO controllers (e.g.  Tsi721).

Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Jean Delvare <jdelvare@suse.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Li Yang <leoli@freescale.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>