[sca] Add KeySideloadFvsr OTBN test

[nasahlpa]

This commit adds the following OTBN SCA routines to the code base:

• init: Init the OTBN SCA test on the device
• init_keymgr: Prepare the keymanager for the OTBN key sideloading test
• key_sideload_fvsr: Start the test
• read_response: Read response from device