[Why]
Secondary viewport dimension/position registers are not programmed,
which can cause issues in some stereo configurations.

[How]
Add register definitions and register programming.
Signed-off-by: NIlya Bakoulin <Ilya.Bakoulin@amd.com>
Reviewed-by: NCharlene Liu <Charlene.Liu@amd.com>
Acked-by: NLeo Li <sunpeng.li@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>