arm64: kconfig: Move LIST_POISON to a safe value

commit bf0c4e04732479f650ff59d1ee82de761c0071f0 upstream.

Move the poison pointer offset to 0xdead000000000000, a
recognized value that is not mappable by user-space exploits.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Thierry Strudel <tstrudel@google.com>
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>