hnvram: Support x86 compiler & changing target_mtd

 - Some minor type changes to support x86 compiler
 - Adds option to read/write to file instead of flash

These changes together allow for unit testing which has been added.

Depends on go/fibercl/XXXXX

In reference to b/31822982

Change-Id: Ica9bfc28fcb6d32361427c9f5ebc56cf0aa6c14c
7 files changed
tree: 4d3b68b4fe5bed81c873bb628742377fe8bd4658
  1. libupgrade/
  2. makehdf