drm/amd/display: Correct cursor position on horizontal mirror

[Why]
Incorrect cursor position will induce system hang on pipe split.

[How]
1.Handle horizontal mirror on rotation,
2.Correct cursor set on piep split.

Reviewed-by: Ariel Bernstein <Eric.Bernstein@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Martin Tsai <martin.tsai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>