[Why]
We manage interrupts for CRTCs in two places:
1. In manage_dm_interrupts(), when CRTC get enabled or disabled
2. When drm_vblank_get/put() starts or kills the vblank counter, calling
   into amdgpu_dm_crtc_set_vblank()

The interrupts managed by these twp places should be identical.

[How]
Since manage_dm_interrupts() already use drm_crtc_vblank_on/off(), just
move all CRTC interrupt management into amdgpu_dm_crtc_set_vblank().

This has the added benefit of disabling all CRTC and HUBP interrupts
when there are no vblank requestors.

Note that there is a TODO item - unchanged from when it was first
introduced - to properly identify the HUBP instance from the OTG
instance, rather than just assume direct mapping.
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>