drm/i915/dp: Enable DP tunnel BW allocation mode

Detect DP tunnels and enable the BW allocation mode on them. Send a
hotplug notification to userspace in response to a BW change.

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240220211841.448846-22-imre.deak@intel.com