Revert "drm/amd/display: dmub_cmd.h: add missing kernel-doc for enums"

Revert "drm/amd/display: dmub_cmd.h: add missing kernel-doc for enums"

[Why & How]
This reverts commit f71d0b68ec58b781f4f44ea642846bedce075e85.

1. Auto-generated Header: The file 'dmub_cmd.h' is an auto-generated header
   managed in an external repository (dmu_stg). Manual changes made directly in
   this repository will be overwritten and lost during the next automated weekly
   synchronization.

2. Tooling Compatibility: This header is governed by internal AMD firmware
   standards which require Doxygen formatting for cross-team documentation.
   Moving to kernel-doc syntax may break internal documentation pipelines.

3. Suppressing Warnings: Current 'make htmldocs' and 'make W=1' builds
   do not actively scan 'dmub_cmd.h' for kernel-doc compliance, thus no warnings
   are triggered during standard compilation. To address warnings generated when
   manually running './scripts/kernel-doc', we have added a notice at the file
   header indicating that this is an auto-generated file that does not strictly
   follow kernel-doc formatting. This ensures that any future linting tools or
   manual checks recognize the formatting as intentional.

Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: James Lin <pinglei.lin@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>