Add sdcardfs variable to storage_config_props

This property allows us to disable sdcardfs if it is present. The old
property ended up getting repurposed, so a new one was needed.
Mediaprovider will also need to access this to determine what actions it
needs to take.

Test: builds
Bug: 155222498
Change-Id: I66ac106613cbb374f54659601e4ba3f61eaecd2f
Merged-In: I66ac106613cbb374f54659601e4ba3f61eaecd2f
8 files changed