sandbox: Allow sched_setaffinity for amd gpu sandbox

This could be called in mesa on some SoCs to set the affinity of the
gallium thread from the main thread.

BUG=b:170305550
TEST=gpu process does not crash

Change-Id: I51aec065750ccbbe71c086ddd2492bc25933d3c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2514066Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Commit-Queue: Drew Davenport <ddavenport@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824755}

sandbox/policy/linux/bpf_cros_amd_gpu_policy_linux.cc

@@ -35,6 +35,7 @@ CrosAmdGpuProcessPolicy::~CrosAmdGpuProcessPolicy() {}
 ResultExpr CrosAmdGpuProcessPolicy::EvaluateSyscall(int sysno) const {
   switch (sysno) {
     case __NR_fstatfs:
+    case __NR_sched_setaffinity:
     case __NR_sched_setscheduler:
     case __NR_sysinfo:
     case __NR_uname: