pseries: Clean up error handling in xics_system_init()
Use the error handling infrastructure to pass an error out from
try_create_xics() instead of assuming &error_abort - the caller is in a
better position to decide on error handling policy.
Also change the error handling from an &error_abort to &error_fatal, since
this occurs during the initial machine construction and could be triggered
by bad configuration rather than a program error.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au> Reviewed-by: Thomas Huth <thuth@redhat.com> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru> Reviewed-by: Markus Armbruster <armbru@redhat.com>