fbdev: Add Kconfig macro FB_IOMEM_HELPERS_DEFERRED

The new Kconfig macro FB_IOMEM_HELPERS_DEFERRED selects fbdev's
helpers for device I/O memory and deferred I/O. Drivers should
use it if they perform damage updates on device I/O memory.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230828132131.29295-4-tzimmermann@suse.de