Next CLs in this stack will make changes to persist/efs mount process
This CL will first move relevant code to a separate file for easier
review.
To support booting under 16K page size, we need to copy files on
persist partition(F2FS, which does not support 16K page size)
to data partition(which will would be EXT4 for dev option enabled
devices).
Bug: 319335586
Change-Id: I2750eb8b53431037cecc972448799409345f5ca3
bb210c9c43