[ARM] Deny user space mappings in first page even on hi-vec CPUs

Don't allow user space mappings in the first page even if we are
using high vectors - this may prevent BUG() from working, as well
as allowing kernel NULL pointer derefs to be silently ignored.

arch/arm/kernel/sys_arm.c

@@ -56,7 +56,7 @@ asmlinkage int sys_pipe(unsigned long __user *fildes)
  * mapping to be mapped at.  This is particularly important for
  * non-high vector CPUs.
  */
-#define MIN_MAP_ADDR	(vectors_high() ? 0 : PAGE_SIZE)
+#define MIN_MAP_ADDR	(PAGE_SIZE)
 
 /* common code for old and new mmaps */
 inline long do_mmap2(