updater: Add a function to check first block

Add and register a function to check if the device has been remounted
since last update during incremental OTA. This function reads block 0
and executes before partition recovery for version >= 4.

Bug: 21124327
Change-Id: I8b915b9f1d4736b3609daa9d16bd123225be357f
(cherry picked from commit 30bf4765593e639966df9f460df22c3fe912e7bf)
2 files changed