[S390] Remove open-coded mem_map usage.

Use page_to_phys and pfn_to_page to avoid open-coded mem_map usage.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
diff --git a/include/asm-s390/page.h b/include/asm-s390/page.h
index 796c400..363ea76 100644
--- a/include/asm-s390/page.h
+++ b/include/asm-s390/page.h
@@ -137,6 +137,7 @@
 #define __pa(x)                 (unsigned long)(x)
 #define __va(x)                 (void *)(unsigned long)(x)
 #define virt_to_page(kaddr)	pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
+#define page_to_phys(page)	(page_to_pfn(page) << PAGE_SHIFT)
 
 #define pfn_valid(pfn)		((pfn) < max_mapnr)
 #define virt_addr_valid(kaddr)	pfn_valid(__pa(kaddr) >> PAGE_SHIFT)