Support a pre-extracted PDK zip

Pre-extracting the zip files are more sustainable for git, so that
objects can be shared if unchanged, rather than the 900MB zip file
changing on every build.

This also has the advantage that we could put an Android.bp file inside
the PDK, and Soong would just pick it up.

Bug: 68767391
Test: Build mini_arm64 PDK with platform.zip
Test: Build mini_arm64 PDK with extracted zip file
Change-Id: I16db030a731aea55b69c1d6e2260dbd70b167544