mm: uninline and cleanup page-mapping related helpers

Most-used page->mapping helper -- page_mapping() -- has already uninlined.
 Let's uninline also page_rmapping() and page_anon_vma().  It saves us
depending on configuration around 400 bytes in text:

   text	   data	    bss	    dec	    hex	filename
 660318	  99254	 410000	1169572	 11d8a4	mm/built-in.o-before
 659854	  99254	 410000	1169108	 11d6d4	mm/built-in.o

I also tried to make code a bit more clean.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>