sim: arm: move arch-specific settings to internal header

There's no need for these settings to be in sim-main.h which is shared
with common/ sim code, so move it all out to a new header which only
this port will include.

The BIT override would be better in the place where it's redefined, so
move it to armdefs.h instead.

sim/arm/arm-sim.h

@@ -0,0 +1,26 @@
+/* Simulation code for the ARM processor.
+   Copyright (C) 2009-2022 Free Software Foundation, Inc.
+
+   This file is part of the GNU simulators.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef ARM_SIM_H
+#define ARM_SIM_H
+
+#include "armdefs.h"
+
+extern struct ARMul_State *state;
+
+#endif