drm/amd/display: Revert logic for plane modifiers

This file was split in commit 5d945cbc
("drm/amd/display: Create a file dedicated to planes") and the logic in
dm_plane_format_mod_supported() function got changed by a switch logic.
That change broke drm_plane modifiers setting on series 5000 APUs
(tested on OXP mini AMD 5800U and HP Dev One 5850U PRO)
leading to Gamescope not working as reported on GitHub[1]

To reproduce the issue, enter a TTY and run:

$ gamescope -- vkcube

With said commit applied it will abort. This one restores the old logic,
fixing the issue that affects Gamescope.

[1](https://github.com/Plagman/gamescope/issues/624

)

Cc: <stable@vger.kernel.org> # 6.0.x
Signed-off-by: Joaquín Ignacio Aramendía <samsagax@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>