[ARM] Prevent oops in free_pages() when freeing a pgd

free_pages() oopses if page->mapping is non-NULL.  Ensure that any
rmap datastructures for the page are freed before freeing the
concerned page.

arch/arm/mm/mm-armv.c

@@ -17,6 +17,7 @@
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
 #include <asm/page.h>
+#include <asm/rmap.h>
 #include <asm/io.h>
 #include <asm/setup.h>
 
@@ -149,6 +150,7 @@ void free_pgd_slow(pgd_t *pgd)
 
 	pte = pmd_page(*pmd);
 	pmd_clear(pmd);
+	pgtable_remove_rmap(pte);
 	pte_free(pte);
 	pmd_free(pmd);
 free: