spapr: Minor cleanups to events handling

spapr: Minor cleanups to events handling

The rtas_error_log structure is marked packed, which strongly suggests its
precise layout is important to match an external interface.  Along with
that one could expect it to have a fixed endianness to match the same
interface.  That used to be the case - matching the layout of PAPR RTAS
event format and requiring BE fields.

Now, however, it's only used embedded within sPAPREventLogEntry with the
fields in native order, since they're processed internally.

Clear that up by removing the nested structure in sPAPREventLogEntry.
struct rtas_error_log is moved back to spapr_events.c where it is used as
a temporary to help convert the fields in sPAPREventLogEntry to the correct
in memory format when delivering an event to the guest.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>