Revert "drm/amd/display: Hardware cursor changes color when switched to software cursor"

This reverts commit 272e6aab.

Applying degamma curve to the cursor by default breaks Linux userspace
expectation.

On Linux, AMD display manager enables cursor degamma ROM just for
implict sRGB on HW versions where degamma is split into two blocks:
degamma ROM for pre-defined TFs and `gamma correction` for user/custom
curves, and degamma ROM settings doesn't apply to cursor plane.

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/1513
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2803


Reported-by: Michel Dänzer <michel.daenzer@mailbox.org>
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4144


Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit f6a305d4)
Cc: stable@vger.kernel.org