[RAPIDIO] Change RapidIO doorbell source and target ID field to 16-bit

Change RapidIO doorbell source and target ID field to 16-bit for
support large system size, which max rio devid is 65535.

Signed-off-by: Zhang Wei <wei.zhang@freescale.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>