BACKPORT: arm64: add seccomp syscall for compat task

This patch allows compat task to issue seccomp() system call.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Bug: 28020023
Patchset: seccomp

(cherry picked from kernel/msm commit 2d9b78ab37c597062cf1cd828df30a3398190452)
Signed-off-by: Kees Cook <keescook@google.com>
Change-Id: I1e490b7aab9cd6ef544f48b0a3be7696ca089562