Backup: Fix IDAC regions after reading whole firmware

Instead of fake reading the IDAC regions, fix them after reading the
whole firmware into a local buffer, but saving to disk.

Plus, refactor the fixup operation itself to make it more flexible.

TEST=confirm that back up file has:
  0x08 from 0x7280-0x72FF
  0x90 from 0x7380-0x747F

Change-Id: Iea115777d9842ccbb83581b1c125f3a59e41d847
1 file changed