libdebugger: ARM fixes for Cortex-A8 and ARM mode.

- Fix destorying the target and thread parts.
- Fix the ARM backend to support Cortex-A8 and ARM mode code.
- Use the DBGDSCR interrupt mask when single stepping.
- Use the DBGDSCR method of entry to debug mode to filter the
  execptions.
- Add support for BSPs to control the ARM backend.

cpukit/libdebugger/rtems-debugger-bsp.c

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2019 Chris Johns <chrisj@rtems.org>.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <rtems/debugger/rtems-debugger-bsp.h>
+
+void* rtems_debugger_arm_debug_registers(void) __attribute__ ((weak));
+bool rtems_debugger_arm_debug_configure(void) __attribute__ ((weak));
+
+void*
+rtems_debugger_arm_debug_registers(void)
+{
+  return NULL;
+}
+
+bool
+rtems_debugger_arm_debug_configure(void)
+{
+  return true;
+}