build: run neverallow checks on platform sepolicy

This will prevent us from breaking our own neverallow rules
in the platform sepolicy regardless of vendor policy adding
exceptions to the neverallow rules using "*_violators" attributes

Bug: 62616897
Bug: 62343727

Test: Build policy for sailfish
Test: Build policy with radio to rild socket rule enabled for all
      and ensure the build fails

Change-Id: Ic66ec3e10c76a7c9a17669e0d3deb3a1c7b00809
Signed-off-by: Sandeep Patil <sspatil@google.com>