drm/amdgpu/dc/mst: Rename dp_mst_stream_allocation(_table)

Just to make this more clear to outside contributors that these are
DC-specific structs, as this also threw me into a loop a number of times
before I figured out the purpose of this.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Fangzhi Zuo <Jerry.Zuo@amd.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220817193847.557945-2-lyude@redhat.com