drm/amd/display: Read Sink emission rate capability

[WHY]
To get sink emission rate information for future
supported refresh rate calculation.

Reviewed-by: ChunTao Tso <chuntao.tso@amd.com>
Signed-off-by: Robin Chen <robin.chen@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>