drm/amd/display: swap system aperture high/low

[why]
Currently logical values are swapped in HW, causing
system aperture to be undefined, so VA and PA cannot co-exist

[how]
program values correctly

Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>