drm/amd/display: on dp link lost event toggle dpms for master pipe only

drm/amd/display: on dp link lost event toggle dpms for master pipe only

[why]
We mistakenly toggle dpms state for non master pipe when handling
link lost. A non master pipe doesn't connect to a backend. So it is
toggling dpms for non master is undefined and caused NULL pointer
dereference.

[how]
Add helper functions to find an array of active master pipes for current
link and only toggle DPMS for active master pipes connected to the link.
Add assert in case we get called to program dpms with non master pipe.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>