Revert "drm/dp_mst: Retrieve extended DPCD caps for topology manager"

Revert "drm/dp_mst: Retrieve extended DPCD caps for topology manager"

This reverts commit ad44c03208e46b83e4ae3269e32c9e524aa71cf8.

Currently DRM driver assume the source device caps is higher than the MST device
caps. With this commit, this statement would be broken.

e.g. the source device only support DP1.2 and the mst device support DP1.4.

Signed-off-by: Koba Ko <koba.ko@canonical.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201103034907.72129-1-koba.ko@canonical.com