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 128950cd72cc3bcb3a57ff417482a5a107ed86bf.

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