drm/amd/display: [FW Promotion] Release 0.0.56

More updates to the comments to better describe the function of
different cmds and parameters in the dmub interface.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>