drm/i915/display: Remove struct drm_fb_helper from struct intel_fbdev

drm/i915/display: Remove struct drm_fb_helper from struct intel_fbdev

Store instances of drm_fb_helper and struct intel_fbdev separately.
This will allow i915 to use the common fbdev client, which allocates
its own instance of struct drm_fb_helper.

There is at most one instance of type each per DRM device, so both can
be referenced directly from the i915 and DRM device structures. A later
patchset might rework the common fbdev client to allow for storing
both, drm_fb_helper and intel_fbdev, together in the same place.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241212170913.185939-9-tzimmermann@suse.de
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>