Update the storage architecture with the new features introduced for
secure element support:
* Lifetime field in key files.
* Slot number in key files for keys in a secure element.
* Transaction file (name and format).
* Persistent storage for secure element drivers (name and format).
The version number is not determined yet.
Switch to the terminology "key file identifier", as has been done in
the code.
The owner uid is now in the upper 32 bits of the key file identifier,
which facilitates namespacing.
Describe the storage format for keys and random seed in Mbed Crypto
0.1.0 released with Mbed OS 5.11, over C stdio and over ITS with
32-bit file identifiers.
Describe the proposed storage format for keys and random seed in the
future release of Mbed Crypto for Mbed OS 5.12, over C stdio and over
ITS with 64-bit file identifiers.
