mm: Make {,set}page_address() static inline if WANT_PAGE_VIRTUAL

{,set}page_address() are macros if WANT_PAGE_VIRTUAL.  If
!WANT_PAGE_VIRTUAL, they're plain C functions.

If someone calls them with a void *, this pointer is auto-converted to
struct page * if !WANT_PAGE_VIRTUAL, but causes a build failure on
architectures using WANT_PAGE_VIRTUAL (arc, m68k and sparc64):

  drivers/md/bcache/bset.c: In function `__btree_sort':
  drivers/md/bcache/bset.c:1190: warning: dereferencing `void *' pointer
  drivers/md/bcache/bset.c:1190: error: request for member `virtual' in something not a structure or union

Convert them to static inline functions to fix this.  There are already
plenty of users of struct page members inside <linux/mm.h>, so there's
no reason to keep them as macros.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>