Allow VNDK extensions under vendor or device

This commit allows VNDK extensions (vndk.enabled:true and vendor:true)
to reside under vendor/* or device/*.  VNDK extensions will be installed
into /vendor/lib[64]/vndk[-sp].  It is reasonable for their source being
under vendor/* or device/*.

Bug: 74506774
Test: lunch aosp_walleye-userdebug && make  # runs unit tests
Change-Id: I406c5bef10f5c549371dd978b8ecc16c65a7af4b