Prevent debugfs unmount on debug builds with a persist property

In order to simplify developer/test flow, the persistent property
persist.dbg.keep_debugfs_mounted can be set to prevent debugfs from
being unmounted on boot.

Bug: 184381659
Test: build and boot
Change-Id: I714616b361e6c8fb59633ec0763f9bd55af7df0e
1 file changed