thunderbolt: Add support for DisplayPort bandwidth allocation mode

The USB4 spec defines an optional feature that allows the connection
manager to negotiate with the graphics through DPCD registers changes in
the bandwidth allocation dynamically. This is referred as "bandwidth
allocation mode" in the spec. The connection manager uses DP IN adapters
registers to communicate with the graphics, and also gets notifications
from these adapters when the graphics wants to change the bandwidth
allocation. Both the connection manager and the graphics driver needs to
support this.

We check if the DP IN adapter supports this and if it does enable it
before establishing a DP tunnel. Then we react on DP_BW notifications
coming from the DP IN adapter and update the bandwidth allocation
accordingly (within the maximum common capabilities the DP IN/OUT
support).

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