drm/amd/display: Fix VTEM InfoPacket programming

Refactor setting bit fields. Correcting the offset of MD0.
Initializing the InfoPacket header fields. Defining the field offsets
and masks.

Signed-off-by: Reza Amini <Reza.Amini@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>