ipr: Add delay to ensure coherent dumps.

Add a holding pattern prior to collecting dump data, to wait for the IOA
indication that the Mailbox register is stable and won't change without
an explicit reset.  This ensures we'll be collecting meaningful dump
data, even when dumping right after an adapter reset.

In the event of a timeout, we still force the dump, since a partial dump
still might be useful.

Signed-off-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
Acked-by: Brian King <brking@linux.vnet.ibm.com>
Reviewed-by: Wen Xiong <wenxiong@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>