FROMLIST: mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT

This configuration variable will be used to build the code needed to
handle speculative page fault.

By default it is turned off, and activated depending on architecture
support, SMP and MMU.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Change-Id: I17123124ec0667a0f0af741a740e5219d278620c
Link: https://lore.kernel.org/lkml/1523975611-15978-2-git-send-email-ldufour@linux.vnet.ibm.com/


Bug: 161210518
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>