drm/amdgpu: Do not implement mode_set_base_atomic callback

drm/amdgpu: Do not implement mode_set_base_atomic callback

Remove all implementations of the CRTC helper mode_set_base_atomic
from amdgpu. It pretends to provide mode setting for kdb debugging,
but has been broken for some time.

Kdb output has been supported only for non-atomic mode setting since
commit 9c79e0b1d096 ("drm/fb-helper: Give up on kgdb for atomic drivers")
from 2017.

While amdgpu provides non-atomic mode setting for some devices, kdb
assumes that the GEM buffer object is at a fixed location in video
memory. This has not been the case since commit 087451f372bf ("drm/amdgpu:
use generic fb helpers instead of setting up AMD own's.") from 2021.
Fbdev-ttm helpers use a shadow buffer with a movable GEM buffer object.
Triggering kdb does not update the display.

Hence remove the whole kdb support from amdgpu.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Acked-by: Daniel Thompson (RISCstar) <danielt@kernel.org>
Link: https://patch.msgid.link/20251125130634.1080966-2-tzimmermann@suse.de