drm/amd/display: [FW Promotion] Release 0.0.51

Add new definition and union for dmub_rb_cmd_dig1_transmitter_control

Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>