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

BugLink: http://bugs.launchpad.net/bugs/1669015
commit d74c67dd7800fc7aae381f272875c337f268806c upstream.

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")
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>