Revert "arcvm: Remove androidboot.selinux=permissive"

This reverts commit 1cafd8a4.

Reason for revert: The CL made SELinux to be enforced even on userdebug images

BUG=b:156699275
TEST=android-sh -c getenforce 

Original change's description:
> arcvm: Remove androidboot.selinux=permissive
> 
> The guest kernel boot parameter is no-op now.
> 
> BUG=None
> TEST=arc.Boot.vm
> 
> Change-Id: I3097b4a8d1276b11d23dd8c436bf10cb3355e9dc
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2191319
> Auto-Submit: Yusuke Sato <yusukes@chromium.org>
> Commit-Queue: Satoshi Niwa <niwa@chromium.org>
> Reviewed-by: Satoshi Niwa <niwa@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#767091}

TBR=yusukes@chromium.org,niwa@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: None
Change-Id: I3d5523a368fce7b08c6b3a9b211a44bcaac27afd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2203349
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Satoshi Niwa <niwa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#769538}

components/arc/session/arc_vm_client_adapter.cc

@@ -176,6 +176,7 @@ std::vector<std::string> GenerateKernelCmdline(
                          start_params.arc_disable_system_default_app),
       "androidboot.chromeos_channel=" + channel,
       "androidboot.boottime_offset=" + MonotonicTimestamp(),
+      "androidboot.selinux=permissive",
   };
   // Since we don't do mini VM yet, set not only |start_params| but also
   // |upgrade_params| here for now.