kasan: introduce inline instrumentation

This patch only demonstration how easy this could be achieved.
GCC doesn't support this feature yet. Two patches required for this:
    https://gcc.gnu.org/ml/gcc-patches/2014-09/msg00452.html
    https://gcc.gnu.org/ml/gcc-patches/2014-09/msg00605.html

In inline instrumentation mode compiler directly inserts code
checking shadow memory instead of __asan_load/__asan_store
calls.
This is usually faster than outline. In some workloads inline is
2 times faster than outline instrumentation.

The downside of inline instrumentation is bloated kernel's .text size:

size noasan/vmlinux
   text     data     bss      dec     hex    filename
11759720  1566560  946176  14272456  d9c7c8  noasan/vmlinux

size outline/vmlinux
   text    data     bss      dec      hex    filename
16553474  1602592  950272  19106338  1238a22 outline/vmlinux

size inline/vmlinux
   text    data     bss      dec      hex    filename
32064759  1598688  946176  34609623  21019d7 inline/vmlinux

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>