drm/amd/display: Explicitly disable cursor when disabling CRTC

[why]
On DCE, the cursor is not being disabled on commits where there is no
CRTC or FB enabled.

[how]
Explicitly disable the cursor in the commit tail only if the pending
commit disables the CRTC.

Signed-off-by: Victor Lu <victorchengchi.lu@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>