Self Tests Must be Repeated Periodically for FIPS Level 3

[nquarton]

For FIPS level 3, 7.10.3.8 requires that self tests are repeated periodically.

Note this requirement does allow deferring self tests when critical services are being performed. To reduce latency during these tests, it may make sense to allow the sequence to be interruptible between each test if a mailbox request is received.

[nquarton]

Open to consider: Is a ROM implementation needed for this? We would not expect ROM to ever be idle long enough for this to run and would prefer to not add anything non-essential in ROM.