accel/tcg: Move CPUNegativeOffsetState into CPUState

Retain the separate structure to emphasize its importance.
Enforce CPUArchState always follows CPUState without padding.

Reviewed-by: Anton Johansson <anjo@rev.ng>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/microblaze/cpu.h

@@ -345,15 +345,15 @@ typedef struct {
 struct ArchCPU {
     /*< private >*/
     CPUState parent_obj;
-
     /*< public >*/
+
+    CPUMBState env;
+
     bool ns_axi_dp;
     bool ns_axi_ip;
     bool ns_axi_dc;
     bool ns_axi_ic;
 
-    CPUNegativeOffsetState neg;
-    CPUMBState env;
     MicroBlazeCPUConfig cfg;
 };