[MIPS] Sibyte: resurrect old cache hack.

The recent switch of the Sibyte SOCs from the processor specific cache
managment code in c-sb1.c to c-r4k.c lost this old hack

    [MIPS] Hack for SB1 cache issues

    Removing flush_icache_page a while ago broke SB1 which was using an empty
    flush_data_cache_page function.  This glues things well enough so a more
    efficient but also more intrusive solution can be found later.
Signed-Off-By: Thiemo Seufer <ths@networkno.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

in the hope it was no longer needed.  As it turns it still is so resurrect
it until there is a better solution.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/c-r4k.c

@@ -7,6 +7,7 @@
  * Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002 Ralf Baechle (ralf@gnu.org)
  * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
  */
+#include <linux/hardirq.h>
 #include <linux/init.h>
 #include <linux/highmem.h>
 #include <linux/kernel.h>
@@ -507,7 +508,11 @@ static inline void local_r4k_flush_data_cache_page(void * addr)
 
 static void r4k_flush_data_cache_page(unsigned long addr)
 {
-	r4k_on_each_cpu(local_r4k_flush_data_cache_page, (void *) addr, 1, 1);
+	if (in_atomic())
+		local_r4k_flush_data_cache_page((void *)addr);
+	else
+		r4k_on_each_cpu(local_r4k_flush_data_cache_page, (void *) addr,
+			        1, 1);
 }
 
 struct flush_icache_range_args {