Bluetooth: Host: Add Encrypted Advertising Data

Create a new Bluetooth library and add Encrypted Advertising Data to it.

Encrypted Advertising Data is a new feature from the Bluetooth Core
Specification 5.4. It provides a way to communicate encrypted data in
advertising, scan response and EIR packets. To do that it introduce a
new advertising data type called `Encrypted Advertising Data`. Also, it
introduce a new characteristic called `Encrypted Data Key Material`,
this provides a way to share the key material.

The library add two main functions `bt_ead_encrypt` and
`bt_ead_decrypt`.

Two helper functions are added to `bluetooth.h`. `bt_data_get_len` and
`bt_data_serialize`, the first one allow the user to get the total size
of a set of `bt_data` structures; the second one generate a spec
compliant bytes array from a `bt_data` structure. The last one is useful
because `bt_ead_encrypt` take as input those kind of bytes array.

Signed-off-by: Théo Battrel <theo.battrel@nordicsemi.no>