drm/radeon: Use mode h/vdisplay fields to hide out of bounds HW cursor

drm/radeon: Use mode h/vdisplay fields to hide out of bounds HW cursor

The crtc_h/vdisplay fields may not match the CRTC viewport dimensions
with special modes such as interlaced ones.

Fixes the HW cursor disappearing in the bottom half of the screen with
interlaced modes.

Fixes: 6b16cf7785a4 ("drm/radeon: Hide the HW cursor while it's out of bounds")
Cc: stable@vger.kernel.org
Reported-by: Ashutosh Kumar <ashutosh.kumar@amd.com>
Tested-by: Sonny Jiang <sonny.jiang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>