vndk-def: Support Treble VNDK directory layout

This commit adds /system/lib/vndk and /vendor/lib/vndk to the search
path for vendor modules.

Bug: 64503245
Test: Run `vndk_definition_tool.py vndk` on the device with Treble VNDK
directory layout.
Test: Run `vndk_definition_tool.py vndk` on sailfish and nothing
changes (including warning/error messages).

Change-Id: Ifb9dd9b21fb93a3c1f2f6d57c61c7416d6437ddb
Merged-In: I7499691c05d66213441371bd18d5b84cf79d6221
(cherry picked from commit 1f01de95)