Add basic verity support to fs_mgr.

This change adds a "verify" fs_mgr flag specifying that
the device in question should be verified.

Devices marked with this flag are expected to have a
footer immediately after their data containing all
the information needed to set up a verity instance.

Change-Id: I10101f2c3240228ee0932e3767fe35e673d2e720
7 files changed