Export DMI enable/active signals for core TAP accesses

[calebofearth]

dmi_mux.v has an uncore_enable signal that gates exported DMI accesses. We request a similar control signal be exported to gate internal core jtag accesses as well. We also request export of a "dmi_active" signal to indicate when the debug module is driving an access.
These reference commits show an implementation of both requests:
chipsalliance/caliptra-rtl@22c08e1
chipsalliance/caliptra-rtl@4117344