ARM: other code uses the new inheritance/nesting scheme

Remove most remaining uses of target->arch_info from ARM
infrastructure, where it hasn't already been updated.

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

src/target/arm7_9_common.h

@@ -108,7 +108,6 @@ typedef struct arm7_9_common_s
 	void (*post_restore_context)(target_t *target); /**< Callback function called after restoring the processor context */
 
 	armv4_5_common_t armv4_5_common;
-	void *arch_info;
 
 } arm7_9_common_t;