Add mechanism for storing mfg info in flash

[terrillmoore]

We want to put the serial number in flash, as a backup for the FRAM storage, and to eliminate printing of the serial number labels. This also gives us some place to put things like calibration values for the analog dividers on the boards. The information for reading at run-time should be in the platform. (Possibly should be moved to the BSP but we can do that later.)

In order to do that, we need data structures, etc.