drm/i915/dp: Handle DP tunnel IRQs

Handle DP tunnel IRQs a sink (or rather a BW management component like
the Thunderbolt Connection Manager) raises to signal the completion of a
BW request by the driver, or to signal any state change related to the
link BW.

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/20240220211841.448846-18-imre.deak@intel.com