sim: invert sim_state storage

Currently all ports have to declare sim_state themselves in their
sim-main.h and then embed the common sim_state_base & sim_cpu in it.
This dynamic makes it impossible to share common object code among
multiple ports because the core data structure is always different.

Let's invert this relationship: common code declares sim_state, and
if the port actually needs state on a per-instance basis, it can use
the new arch_data field for it.  Most ports don't actually use it,
so they don't need to declare anything at all.

This is the first in a series of changes: it adds a define to select
between the old & new layouts, then converts all the ports that don't
need custom state over to the new layout.

sim/mcore/sim-main.h

@@ -19,6 +19,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef SIM_MAIN_H
 #define SIM_MAIN_H
 
+#define SIM_HAVE_COMMON_SIM_STATE
+
 #include "sim-basics.h"
 
 typedef long int           word;
@@ -68,12 +70,5 @@ struct _sim_cpu {
   sim_cpu_base base;
 };
 
-struct sim_state {
-
-  sim_cpu *cpu[MAX_NR_PROCESSORS];
-
-  sim_state_base base;
-};
-
 #endif