vboot: cgpt: Support writing GPT structs to NOR flash

This CL allows the GPT headers and partition entry arrays to be stored
in a NOR flash device. Instead of treating both the NOR and NAND devices
as one (in a sandwich way), this CL writes and reads the GPT structs
independently of the actual device that houses the partitions.
Therefore, the first usable LBA of the partitions will be at 0, and the
last usable LBA is at the end of the NAND.

  | NOR houses GPT structs |
  0     |  Index into
  v     v
  | NAND houses partitions |

Note that the "my_lba", "alternate_lba", "entries_lba" in the GPT headers
are no longer meaningful.

Consumers of cgptlib will have to set "stored_on_device" to either
GPT_STORED_ON_DEVICE or GPT_STORED_OFF_DEVICE, and "gpt_drive_sectors"
to the number of 512-byte sectors available to store GPT structs.

The NOR read and write operations are done by "flashrom".

TEST=build with DEBUG, cgpt create/add/show on a stumpy-moblab

Change-Id: I083b3c94da3b0bb3da1a7b10c6969774080a2afd
Reviewed-on: https://chromium-review.googlesource.com/226800
Reviewed-by: Nam Nguyen <namnguyen@chromium.org>
Commit-Queue: Nam Nguyen <namnguyen@chromium.org>
Tested-by: Nam Nguyen <namnguyen@chromium.org>
15 files changed