drm/i915/mst: update max stream count to match number of pipes

drm/i915/mst: update max stream count to match number of pipes

We create the stream encoders and attach connectors for each pipe we
have. As the number of pipes has increased, we've failed to update the
topology manager maximum number of payloads to match that. Bump up the
max stream count to match number of pipes, enabling the fourth stream on
platforms that support four pipes.

Cc: stable@vger.kernel.org
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250226135626.1956012-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>