seccomp: revert previous patches in prep for updated ones

This reverts the seccomp related patches committed around 2014-08-27.
This allows for a cleaner cherry-pick of newly landed upstream patches.

 f56b1aa3 arm: fixup NR_syscalls to accommodate the new seccomp syscall
 81ff7fa2 seccomp: implement SECCOMP_FILTER_FLAG_TSYNC
 d9247279 seccomp: allow mode setting across threads
 743266ae seccomp: introduce writer locking
 3497a88f seccomp: split filter prep from check and apply
 2c6d7de5 MIPS: add seccomp syscall
 83f1ccba ARM: add seccomp syscall
 a75a29b1 seccomp: add "seccomp" syscall
 1a63bcec seccomp: split mode setting routines
 c208e4e9 seccomp: extract check/assign mode helpers
 6862b014 seccomp: create internal mode-setting function
 1ba2ccbc MAINTAINERS: create seccomp entry
 c2da3eba seccomp: fix memory leak on filter attach
 945a225e ARM: 7888/1: seccomp: not compatible with ARM OABI

Change-Id: I3f129263d68a7b3c206d79f84f7f9908d13064f6
Signed-off-by: JP Abgrall <jpa@google.com>