core/cpu: parallelise global CPU register setting jobs
core/cpu: parallelise global CPU register setting jobs

On a 176 thread system, before:

[  122.319923233,5] OPAL: Switch to big-endian OS
[  126.317897467,5] OPAL: Switch to little-endian OS

after:

[  212.439299889,5] OPAL: Switch to big-endian OS
[  212.469323643,5] OPAL: Switch to little-endian OS

Signed-off-by: Nicholas Piggin <24829078df5003d9dd1dd871ca2aeb0b1cf95ef4@gmail.com>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.ibm.com>

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