Add prlog_once for logging a message only once
Add prlog_once for logging a message only once

Signed-off-by: Joel Stanley <4816dabf8db1bc6cac35b3a24cab2ff844b5b0c7@jms.id.au>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

mikey/skiboot,legoater/skiboot,open-power/skiboot,apopple/skiboot,shenki/skiboot,qemu/skiboot,legoater/skiboot,qemu/skiboot,apopple/skiboot,open-power/skiboot,apopple/skiboot,qemu/skiboot,stewart-ibm/skiboot,legoater/skiboot,ddstreet/skiboot,legoater/skiboot,ddstreet/skiboot,stewart-ibm/skiboot,open-power/skiboot,stewart-ibm/skiboot,csmart/skiboot,mikey/skiboot,shenki/skiboot,shenki/skiboot,open-power/skiboot,shenki/skiboot,ddstreet/skiboot,open-power/skiboot,legoater/skiboot,qemu/skiboot,csmart/skiboot,mikey/skiboot,qemu/skiboot,shenki/skiboot,csmart/skiboot