drm/i915/ddi: write payload for 128b/132b SST

Write the payload allocation table for 128b/132b SST. Use VCPID 1 and
start from slot 0, with dp_m_n.tu slots.

This is preparation for enabling 128b/132b SST. This path is not
reachable yet. Indeed, we don't yet compute TU for 128b/132b SST.

v2: Handle drm_dp_dpcd_write_payload() failures (Imre)

v3: Include drm_dp_helper.h (kernel test robot)

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250107095414.1244286-1-jani.nikula@intel.com