Bootrom Tools: Added a nuttx->ffff packer
Bootrom Tools: Added a nuttx->ffff packer

Added nuttx2ffff, and fixed some errors and shortcomings in the existing
code that was exposed during the bringup. (Incorporated Greg's review
feedback and some operational feedback from Fabien)

Expanded Readme.md to direct the reader to "makeall" as the means of
creating a simple 3-stage boot "hello world" app.

Testing Done: verified that it will work correctly
Bug Number: trivial
Review URL: https://reviews.leaflabs.com/r/2202/
Reviewed by: Greg HK

Signed-off-by:  Morgan Girling <980e61e2e2b82c453db57c2e8646c01fbd3318cd@bsquare.com>

gregkh/bootrom-tools,projectara/bootrom-tools,gregkh/bootrom-tools,projectara/bootrom-tools,gregkh/bootrom-tools,projectara/bootrom-tools