drm/amd/display: Program CURSOR_DST_X_OFFSET in viewport space

[WHAT & HOW]
According to register specifications, the CURSOR_DST_X_OFFSET
is relative to the start of the data viewport, not RECOUT space.
In this case we must transform the cursor coordinates passed to
hubp401_cursor_set_position into viewport space to program this
register. This fixes an underflow issue that occurs in scaled
mode with low refresh rate.

Reviewed-by: Nevenko Stupar <nevenko.stupar@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>