arm64: kasan: Add cpu_supports_tags helper

Add an arm64 helper called cpu_supports_mte() that exposes information
about whether the CPU supports memory tagging and that can be called
during early boot (unlike system_supports_mte()).

Use that helper to implement a generic cpu_supports_tags() helper, that
will be used by hardware tag-based KASAN.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://linux-review.googlesource.com/id/Ib4b56a42c57c6293df29a0cdfee334c3ca7bdab4