spapr: Add RTAS sysparm UUID

Add support for the UUID parameter to the emulated RTAS call
ibm,get-system-parameter.

Return the guest's UUID as the value for the RTAS UUID system
parameter, or null (a zero length result) if it is not set.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index d043771..46b7a71 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -399,6 +399,7 @@
 
 /* RTAS ibm,get-system-parameter token values */
 #define RTAS_SYSPARM_DIAGNOSTICS_RUN_MODE        42
+#define RTAS_SYSPARM_UUID                        48
 
 /* Possible values for the platform-processor-diagnostics-run-mode parameter
  * of the RTAS ibm,get-system-parameter call.