Add skiboot-5.4.6 release notes
Add skiboot-5.4.6 release notes

Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>
(cherry picked from commit cf81313413067463d312198b7bf74c654a8f4396)
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

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