Support :vndk requirement from /product partition

linkerconfig can now distinguish /product/apex from /vendor/apex.
So, it provides correct version of VNDK to vendor apexes.

Bug: 159576928
Test: atest --host linkerconfig_diff_test
Change-Id: Ib11dd1c51a6b9e0c875edab12bb37026e33a80cc
3 files changed