FIX: add 'function' to top-level dbdtree node list

[klauer]

Unless our generated database definition is malformed, the pypdb top-level entries in pyPDB.dbdlint.dbdtree appear to be missing 'function':

For example, from our IOC's built .dbd file:

registrar(asynInterposeEosRegister)
...
function(scanMon)
function(rebootProc)
function(scanMonInit)

This leads to linter errors:

Unknown node or out of context: Block(function, ['scanMonInit'], None)

[mdavidsaver]

oops... I didn't notice that this was a PR and fixed with almost identical d745811

[klauer]

Thanks