drm/amd/display: 3.2.308

This version brings along following fixes:
- Prune Invalid Modes for HDMI Output
- SPL Cleanup
- Fix brightness level not retained over reboot
- Remove inaccessible registers from DMU diagnostics

Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>