edgeos: enable CONFIG_USERFAULTFD

BUG=b/352751487
TEST=emerge and verified in qemu that flag is set
RELEASE_NOTE=n/a

Change-Id: Iac0ba434bf3453a80b70f25df429cceaf6f637b8
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/77879
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Trevor Schroeder <trevors@google.com>
Reviewed-by: Scott Haiden <scotthaiden@google.com>