Revert "Revert "BACKPORT: FROMLIST: ext4: implement speculative fault handling""

This reverts commit 7a67b48b.
The original commit was reverted due to the issue in speculative
handling of file-backed pages. Now that the fix is implemented by
disabling interrupts when walking the page tables this functionality
can be re-enabled.

Bug: 245389404
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: Ib33a02757eaab60e829941ccfd0f9caa15991282