seccomp: sisupdate.update.policy: Limit mmap and mprotect arg2.

We do not want to allow writable executable memory.

BUG=b:172212144
TEST=manual check

Change-Id: If07efd9bd98b6e38ecf386b7bb5a981aa540bcf6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/touch_updater/+/3945859
Commit-Queue: Allen Webb <allenwebb@google.com>
Tested-by: Sean O'Brien <seobrien@chromium.org>
Tested-by: Allen Webb <allenwebb@google.com>
Reviewed-by: Sean O'Brien <seobrien@chromium.org>
1 file changed