kasan: simplify address description logic

Simplify logic for describing a memory address.  Add addr_to_page()
helper function.

Makes the code easier to follow.

Change-Id: I082260f2dce212c35afbda57a7f327d1b9bb5a1f
Link: http://lkml.kernel.org/r/20170302134851.101218-5-andreyknvl@google.com


Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: db429f16e0b472292000fd53b63ebd7221a9856e
Git-repo: http://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Trilok Soni <tsoni@codeaurora.org>