drm/amd/display: panel inst for monitors

drm/amd/display: panel inst for monitors

[WHY]
To find proper panel replay panel inst for external monitors.

[HOW]
Use otg index as panel replay panel inst.
Both Replay features use the same logic to get panel inst.
Correct the bug that would overwrite panel inst in cmd

Reviewed-by: Robin Chen <robin.chen@amd.com>
Signed-off-by: Peichen Huang <PeiChen.Huang@amd.com>
Signed-off-by: Matthew Stewart <matthew.stewart2@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>