vndk-def: Implement VNDK-SP-Ext collection

This commit implements the VNDK-SP-Ext properly so that the output will
copy missing VNDK-SP-Indirect to /vendor/lib[64]/vndk-sp.

Bug: 37867089
Bug: 37940694
Test: Add/remove generic reference dump and make sure vndk-sp libs will
be listed as extra_vndk_sp_indirect.

Merged-In: I76bc41e189e566c66c6f96db9555d366921b7995
(cherry picked from commit 489dabb2)

Change-Id: Ief1cc42f6d1684879b096b3fc49f7f58fdfa4004