sh: stub __flush_tlb_global() definition for nommu.

This fixes up the nommu build with a stub definition for
__flush_tlb_global(), now used by the reboot code.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/mm/nommu.c b/arch/sh/mm/nommu.c
index 7694f50..36312d2 100644
--- a/arch/sh/mm/nommu.c
+++ b/arch/sh/mm/nommu.c
@@ -67,6 +67,10 @@
 	BUG();
 }
 
+void __flush_tlb_global(void)
+{
+}
+
 void __update_tlb(struct vm_area_struct *vma, unsigned long address, pte_t pte)
 {
 }