Check settings of severity state fields in zero field

The zero field mbbo STATUS PV has e.g. ONSV defined as "INVALID" but according to the documentation at https://epics.anl.gov/base/R7-0/4-docs/mbboRecord.html this is not supported for the STATE alarm that is raised - only MINOR, MAJOR or NO_ALARM are allowed. It might be this works currently, but we should bring it into line with what is supported. It seems reasonable to exclude INVALID alarm, that would mean we didn't know the value, but we do actually know the value and wish to raise an alarm based on it.

## Acceptance Criteria

- mbbo state fields corrected
- search of other epics records in repositories for similar issues and tickets created as necessary