drm/msm/dp: decouple link and stream configuration

Decouple the dp link and stream configurations.
Configuring the data stream along with link config works
fine in SST mode as only one stream present on SST link.
MST mode supports more than one stream on a single link.
The link config is required only once and data stream
config happens whenever a new stream is turned on and off.

CRs-Fixed: 2192818
Change-Id: Ifa4275cc5ad6c032176a5ae51faab37bf06270b0
Signed-off-by: Govinda Rajulu Chenna <gchenna@codeaurora.org>