drm: Remove the legacy DRM_IOCTL_MODESET_CTL ioctl

DRM drivers with user-space mode setting have been removed in Linux
v6.3. [1] Now remove the ioctl entry points for these drivers. Invoking
any of the ioctl ops will unconditionally return -EINVAL to user space.

Invoking DRM_IOCTL_MODESET_CTL is different from the other legacy
ioctl ops as it returns 0 even without CONFIG_DRM_LEGACY set. From the
original commit 29935554 ("drm: Disallow DRM_IOCTL_MODESET_CTL for
KMS drivers") it is not apparent how or why the operation differs from
the others. It is likely just an oversight in commit 61ae2270


("drm: allow removal of legacy codepaths (v4.1)"), which allowed
disabling leagacy ioctls in the first place. Still keep this removal
separate from the other ioctls to allow an easy revert, if necessary.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/series/111602/ # [1]
Reviewed-by: David Airlie <airlied@gmail.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231122122449.11588-10-tzimmermann@suse.de