Also add steps to disable flash encryption, as some people seem to
accidentally enable it.
Explicitly mark the flash encryption and secure boot as "READ DOCS
FIRST" in menuconfig.
Seems doing certain kinds of short reads while flash encryption is
enabled will return stale data. This fixes it, but is probably a
little heavy-handed performance wise.
* App access functions are all flash encryption-aware
* Documentation for flash encryption
* Partition read/write is flash aware
* New encrypted write function
