thunderbolt: Rework how tunnel->[init|deinit] hooks are called

The way these are called is not exactly symmetric as it is supposed to
be: the former is called when tunnel is being activated and the latter
is called when it is being released (not when it is being de-activated).

Furthermore host-to-host (DMA) tunnels are abusing the ->deinit hook to
clear out the credits. This makes it quite hard to follow what is being
called and when.

For these reasons rework the two "init" hooks to be called symmetrically
and rename them accordingly. For the DMA one, add a new hook that is
specifically used to run clean up for the tunnel when its memory is
being released.

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