drm/msm/dp: do not toggle clocks for link maintenance

If the link maintenance request is received from sink
after video stream has been activated, re-do link
training without switching off/on the link and stream
clocks. Toggling clocks while an active stream is going
on results in V-sync timeout and may result in an unstable
display engine. As DisplayPort controller can handle
dynamic switching between video stream and link patterns
without interrupting V-sync, complete link training without
toggling clocks.

CRs-Fixed: 2309587
Change-Id: Iba8d1efb7041e9c82e08d9ba3e2aa82700e24d1c
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>