drm/amd/display: Fix dig register undefined

[Why]
Some of the stream encoder registers have register offset address 0. It
is causing no display in some scenarios due to DIG_FE was not setup
correctly and was not enabled.

[How]
Fix stream encoder register define list.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Duncan Ma <duncan.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>