amd/display: remove ChromeOS workaround

This reverts commits ddab8bd7 ("drm/amd/display: Fix two cursor duplication
when using overlay") and e7d9560a

 ("Revert "drm/amd/display: Fix overlay
validation by considering cursors"").

tl;dr ChromeOS uses the atomic interface for everything except the cursor. This
is incorrect and forces amdgpu to disable some hardware features. Let's revert
the ChromeOS-specific workaround in mainline and allow the Chrome team to keep
it internally in their own tree.

See [1] for more details. This patch is an alternative to [2], which added
ChromeOS detection.

[1]: https://lore.kernel.org/amd-gfx/JIQ_93_cHcshiIDsrMU1huBzx9P9LVQxucx8hQArpQu7Wk5DrCl_vTXj_Q20m_L-8C8A5dSpNcSJ8ehfcCrsQpfB5QG_Spn14EYkH9chtg0=@emersion.fr/
[2]: https://lore.kernel.org/amd-gfx/20211011151609.452132-1-contact@emersion.fr/

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Sean Paul <seanpaul@chromium.org>
Fixes: ddab8bd7 ("drm/amd/display: Fix two cursor duplication when using overlay")
Fixes: e7d9560a

 ("Revert "drm/amd/display: Fix overlay validation by considering cursors"")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>