libmedia2_jni: use libbinder as shared library

In order to prevent prebuilts from freezing the libbinder
internal API (the wire protocol), it is being made a
shared-only library.

Bug: 111454508
Test: m only
Change-Id: If7f8bd931dae5310eda6c230f20179418c2efa43
(cherry picked from commit a192e0e3)
Merged-In: If7f8bd931dae5310eda6c230f20179418c2efa43