add seccomp syscall for compat task

Note: This patch is from v6 of Takahiro's proposed
"arm64: add seccomp support" patchset (leecam@google.com)

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

Signed-off-by: AKASHI Takahiro <takahiro.akashi <at> linaro.org>
Git-commit: 4f12b53f28a751406a27ef7501a22f9e32a9c30b
Git-repo: https://android.googlesource.com/kernel/common.git


[imaund@codeaurora.org: Resolved conflicts caused by sched_setattr and
sched_getattr already being enabled in our baseline]
Signed-off-by: Ian Maund <imaund@codeaurora.org>

Change-Id: I946add85f22dc928e6c807afff439b5830fcf47b
Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>