opal/hmi: Report NPU2 checkstop reason
opal/hmi: Report NPU2 checkstop reason

The NPU2 is currently not passing any information to linux to explain
the cause of an HMI. NPU2 has three Fault Isolation Registers and over
30 of those FIR bits are configured to raise an HMI by default. We
won't be able to fit all possible state in the 32-bit xstop_reason
field of the HMI event, but we can still try to encode up to 4 HMI
reasons.

Signed-off-by: Frederic Barrat <c90240987c583ac0802fbeb88cb1684edc683e18@linux.ibm.com>
Reviewed-by: Andrew Donnellan <44ca8c041ed925606732b2a0f30e5b73c32761a8@linux.ibm.com>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.ibm.com>

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