drm/amd/display: Optimize cursor position updates

drm/amd/display: Optimize cursor position updates

[why]
Updating the cursor enablement register can be a slow operation and accumulates
when high polling rate cursors cause frequent updates asynchronously to the
cursor position.

[how]
Since the cursor enable bit is cached there is no need to update the
enablement register if there is no change to it.  This removes the
read-modify-write from the cursor position programming path in HUBP and
DPP, leaving only the register writes.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Sung Lee <sung.lee@amd.com>
Signed-off-by: Aric Cyr <Aric.Cyr@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>