Only create one ITS configuration table

When there are multiple ITS devices in the system we would allocate a
configuration table for each, however only one table is needed as all the
ITS devices share this.

Allocate a table only when the global table is unset.

While here fix the type of this to be a pointer to a uint8_t array as the
entries are all 8 bits wide.

MFC after: 2 weeks
Sponsored by: DARPA, AFRL