Add multilib.prefer32.deps to packaging base

The property is used to prefer the 32-bit variant of a dep over the
64-bit variant. If 64-bit variant is the only available one, it is
depended on.

This will be used to include 32-bit preferred modules like drmserver and
mediaserver in filesystem modules.

Bug: N/A
Test: go test ./... under soong/android

Change-Id: Ic7185eb2044c9987f8d1e9b6cf7f0dbd235cf04c