Fix a few missing dependencies in APEX building

I found these while trying to build an aosp_arm system image with RBE,
which only makes the sources that you depend on available to every rule.

The hardcoded prebuilts/sdk path is a bit unfortunate, but that's
currently hardcoded as a default in the script as well.

Bug: 130111713
Test: treehugger
Test: build a system image with RBE
Change-Id: I4415563017e053749788b0a537a48d61a2161935