x86, kfence: enable KFENCE for x86

x86, kfence: enable KFENCE for x86

Add architecture specific implementation details for KFENCE and enable
KFENCE for the x86 architecture. In particular, this implements the
required interface in <asm/kfence.h> for setting up the pool and
providing helper functions for protecting and unprotecting pages.

For x86, we need to ensure that the pool uses 4K pages, which is done
using the set_memory_4k() helper function.

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Co-developed-by: Marco Elver <elver@google.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Jann Horn <jannh@google.com>
[port kfence feature to rpi-5.10.95]
Signed-off-by: Sung-hun Kim <sfoon.kim@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: Idfebe6e03d9bda5de4bd6d0084f65bd0feda8d8a