ARM7/ARM9: use shared examine() method

No point in having two identical examine methods for the
ARM7TDMI and ARM9TDMI drivers; move, rename, shrink, share.

Add a bit of doxygen; stop needlessly exporting a method.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/arm920t.c

@@ -1420,7 +1420,7 @@ struct target_type arm920t_target =
 	.register_commands = arm920t_register_commands,
 	.target_create = arm920t_target_create,
 	.init_target = arm9tdmi_init_target,
-	.examine = arm9tdmi_examine,
+	.examine = arm7_9_examine,
 	.mrc = arm920t_mrc,
 	.mcr = arm920t_mcr,
 };