Fix enum undef ts bug35

[bhill-slac]

When support for propEventCB was added to the gateway, it subscribed to DBR_CTRL_* but calls both runDataCB and runValueDataCB. Since the DBR_CTRL_* events have zero in the timestamp fields and the value_data_callbacks assign the gdd from the DBR_CTRL* event to the gatePv value gdd, it can step on the timestamp from the DBR_TIME_* event.

I suspect the code in gatePvData::propEventCB was ignoring the first propEvent to avoid this bug but some cases get through and set the timestamp fields to zero, in particular mbbi and mbbo records.

This fix creates to subcriptions for DBE_PROPERTY events, one DBR_CTRL* subscription w/ propDataCB, and a DBR_TIME* subscription w/ propEventCB.