drm/amd/display: Disable cursor when offscreen in negative direction

[Why]
When x or y is negative we set the x and y values to 0 and compensate
with a positive cursor hotspot in DM since DC expects positive cursor
values.

When x or y is less than or equal to the maximum cursor width or height
the cursor hotspot is clamped so the hotspot doesn't exceed the
cursor size:

if (x < 0) {
        xorigin = min(-x, amdgpu_crtc->max_cursor_width - 1);
        x = 0;
}

if (y < 0) {
        yorigin = min(-y, amdgpu_crtc->max_cursor_height - 1);
        y = 0;
}

This incorrectly forces the cursor to be at least 1 pixel on the screen
in either direction when x or y is sufficiently negative.

[How]
Just disable the cursor when it goes far enough off the screen in one
of these directions.

This fixes kms_cursor_crc@cursor-256x256-offscreen.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Sun peng Li <Sunpeng.Li@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>