drm/i915/display: Move fbdev code around

Move fbdev code around in the source file before switching to DRM's
generic fbdev client. This will make the conversion less intrusive.
No functional changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241212170913.185939-10-tzimmermann@suse.de


Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>