drm/amd/display: avoid disable otg when dig was disabled

[Why]
This is a workaround for an dcn3.15 hang
that happens if otg dispclk is ramped while
otg is on and stream enc is off. But this
w/a should not trigger when we have a dig active.

[How]
Avoid disable otg when dig was disabled.

[Note]
Reapplying commit b07bb766 ("drm/amd/display: avoid disable otg when dig was disabled")
which was incorrectly reverted.

Reviewed-by: Josip Pavic <Josip.Pavic@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Jingwen Zhu <Jingwen.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>