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/sparc/cpu.h

@@ -561,7 +561,6 @@ struct ArchCPU {
     CPUState parent_obj;
     /*< public >*/
 
-    CPUNegativeOffsetState neg;
     CPUSPARCState env;
 };