arm64/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT

Set ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT for arm64. This
enables Speculative Page Fault handler.

Change-Id: Ic55bd1993b3af78ddac25867c5f422861079bb27
Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
Patch-mainline: linux-mm @ Wed, 2 May 2018 15:54:31
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>