drm/amd/display: Add ENGINE_ID_DIGD condition check for Navi14

[Why]
Navi10 has 6 PHY, but Navi14 only has 5 PHY, that is
because there is no ENGINE_ID_DIGD in Navi14. Without
this patch, many HDMI related issues (e.g. HDMI S3
resume failure, HDMI pink screen on boot) will be
observed.

[How]
If "eng_id" is larger than ENGINE_ID_DIGD, then
add "eng_id" by 1.

Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>