blackfin: Wire up missing syscalls

The related syscalls are below which may cause samples/kdbus building
break in next-20150401 tree, the related information and error:

    CALL    scripts/checksyscalls.sh
  <stdin>:1223:2: warning: #warning syscall kcmp not implemented [-Wcpp]
  <stdin>:1226:2: warning: #warning syscall finit_module not implemented [-Wcpp]
  <stdin>:1229:2: warning: #warning syscall sched_setattr not implemented [-Wcpp]
  <stdin>:1232:2: warning: #warning syscall sched_getattr not implemented [-Wcpp]
  <stdin>:1235:2: warning: #warning syscall renameat2 not implemented [-Wcpp]
  <stdin>:1238:2: warning: #warning syscall seccomp not implemented [-Wcpp]
  <stdin>:1241:2: warning: #warning syscall getrandom not implemented [-Wcpp]
  <stdin>:1244:2: warning: #warning syscall memfd_create not implemented [-Wcpp]
  <stdin>:1247:2: warning: #warning syscall bpf not implemented [-Wcpp]
  <stdin>:1250:2: warning: #warning syscall execveat not implemented [-Wcpp]
  [...]
    HOSTCC  samples/kdbus/kdbus-workers
  samples/kdbus/kdbus-workers.c: In function ‘prime_new’:
  samples/kdbus/kdbus-workers.c:930:18: error: ‘__NR_memfd_create’ undeclared (first use in this function)
    p->fd = syscall(__NR_memfd_create, "prime-area", MFD_CLOEXEC);
                    ^
  samples/kdbus/kdbus-workers.c:930:18: note: each undeclared identifier is reported only once for each function it appears in

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>