MTD shim layer for RAMTRON FRAM file interface

This adds full support for parameters and waypoints (on two 8K files as default) on RAMTRON FRAM (on PX4FMUv2.x as used in Pixhawk).

This is sufficient for ~3500 parameters and 200 waypoints. We might want to distribute space slightly differently (e.g. 4K / 12K) which is easily possible.

Testing would be appreciated. There is a basic level of error checking in the BSON decoding, so it should be kind of safe to use.