entity-manager: move post_process to do_compile

Move the post_process script so that we can keep the
output directory good. Meanwhile, we can choose what we
want to install in the do_install phase.

Google-Bug-Id: 441445178
Tested: included succesfully
Fusion-Link:
platform11: fusion2/54582970-3115-322d-917e-6d11c1a227bd
platform5: fusion2/fb6f53b1-a2bc-3454-8fa1-f5346a57358e
platform15: fusion2/37e8284c-d111-3317-851d-22a785df7679
platform17: fusion2/242359ad-c95e-373f-925a-758c26ce713e
Change-Id: I2a5d3c31dfcbd5425827c73b630f676f6378d9fd
Signed-off-by: Alex Lai <alexlai@google.com>
(cherry picked from commit 60bce29a0e5ab8d7641e4546417c50cc866ae19d)
Platforms-Affected: All