[Skiboot] skiboot-5.0-rc2 tagged

[Stewart Smith]

Really small set of changes from skiboot-5.0-rc1 to skiboot-5.0-rc2,
although important for opal-prd, IPMI boot count sensor and correctly
loading LIDs on FSP machines.

Patches merged:
 opal: Fix an issue where partial LID load causes opal to hang.
 nx: use proc_gen instead of param
 use chip id for NX engine Coproc Instance num
 Fix (hopefully) missing dot symbols in skiboot.map
 exceptions: Catch exceptions at boot time
 exceptions: Remove deprecated exception patching stuff
 mambo: Make mambo_utils.tcl optional
 mambo: Exit mambo when the simulation is stopped
 add NX register defines
 set NX crb input queues to 842 only
 core: Catch attempts to branch through a NULL pointer
 plat/firestone: Add missing platform hooks
 plat/firestone: Add missing platform hooks
 elog: Don't call uninitialized platform elog_commit
 external/opal-prd: Use "official" switch-endian syscall
 hw/ipmi: Rework sensors and fix boot count sensor


Testing, as always, is very much appreciated.