sepolicy: make exec_types in /vendor a subset of vendor_file_type

We install all default hal implementations in /vendor/bin/hw along with
a few domains that are defined in vendor policy and installed in
/vendor. These files MUST be a subset of the global 'vendor_file_type'
which is used to address *all files installed in /vendor* throughout the
policy.

Bug: 36463595
Test: Boot sailfish without any new denials

Change-Id: I3d26778f9a26f9095f49d8ecc12f2ec9d2f4cb41
Signed-off-by: Sandeep Patil <sspatil@google.com>