x86: kmsan: enable KMSAN builds for x86

Make KMSAN usable by adding the necessary Kconfig bits.

Also declare x86-specific functions checking address validity
in arch/x86/include/asm/kmsan.h.

Signed-off-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Marco Elver <elver@google.com>
2 files changed