sepolicy: Fix renderscript driver lookup

Renderscript drivers are loaded from /vendor/lib64 by following the
/system/vendor symlink. This change fixes a couple of things.
- Allows all domains access to follow the symlink
- Restores app domain permissions for /vendor for non-treble devices
- Allow app domains to peek into /vendor/lib64, but NOT grant 'execute'
  permissions for everything. Since RS drivers can be loaded into any
  process, their vendor implementation and dependencies have been
  marked as 'same process HALs' already.

Bug: 37169158
Test: Tested on sailfish (Treble) & Angler (non-treble)
      ./cts-tradefed run cts -m CtsRenderscriptTestCases \
      --skip-device-info --skip-preconditions --skip-connectivity-check \
      --abi arm64-v8a
      Result: Tests Passed: 743 Tests Failed: 0

Change-Id: I36f5523381428629126fc196f615063fc7a50b8e
Signed-off-by: Sandeep Patil <sspatil@google.com>