thunderbolt: Change TMU mode to HiFi uni-directional once DisplayPort tunneled

Here we configure TMU mode to HiFi uni-directional once DP tunnel
is created. This is due to accuracy requirement for DP tunneling
as appears in CM guide 1.0, section 7.3.2.
Due to Intel hardware limitation, once we changed the TMU mode to HiFi
uni-directional (when DP tunnel exists), we don't change TMU mode back to
normal uni-directional, even if DP tunnel is torn down later.

Signed-off-by: Gil Fine <gil.fine@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>