x86_64: add hint on GPF if CONFIG_KASAN_INLINE=y

Add kasan's die notifier which prints a hint message
before General protection fault, explaining that GPF
could be caused by NULL-ptr dereference or user memory access

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
x86_64: kasan: rename kasan_map_shadow() to kasan_init().

Now kasan_map_shadow() do few more things that just maps
shadow memory. So kasan_init() sounds like a better name for it.
Also move call to this function from zone_sizes_init to setup_arch().
IMO it's more appropriate thing for it.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
kasan: slightly tweak report.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Merge pull request #16 from aryabinin/kasan

Few minor updates