Add manifest flag to enable prerelease driver.

Add manifest flag to prevent applications from using prerelease driver
accidentally. In this patch we also allow any debuggable device build to load
prerelease driver for all non-system and non-privileged applications.

BUG: 138132808
Test: Verified with prerelease driver.
Change-Id: If0abc89f709c8e34bd83a5c09c3c2047300b5ef2