sim: watchpoints: use common sim_pc_get

Few arches implement STATE_WATCHPOINTS()->pc while all of them implement
sim_pc_get.  Lets switch the sim-watch core for monitoring pc events to
the sim_pc_get API so this module works for all ports, and then we can
delete this old back channel of snooping in the port's cpu state -- the
code needs the pointer to the pc storage so that it can read out bytes
and compare them to the watchrange.

This also fixes the logic on multi-cpu sims by removing the limitation
of only being able to watch CPU0's state.

sim/avr/interp.c

@@ -1690,12 +1690,6 @@ sim_open (SIM_OPEN_KIND kind, host_callback *cb,
       return 0;
     }
 
-  {
-    /* XXX: Only first core gets profiled ?  */
-    SIM_CPU *cpu = STATE_CPU (sd, 0);
-    STATE_WATCHPOINTS (sd)->pc = &cpu->pc;
-  }
-
   if (sim_pre_argv_init (sd, argv[0]) != SIM_RC_OK)
     {
       free_state (sd);