fbdev/arcfb: Use generator macros for deferred I/O

Implement the driver's fops with the generator macros for deferred
I/O. Only requires per-driver code for the on-scren scanout buffer.
The generated helpers implement reading, writing and drawing on top
of that. Also update the selected Kconfig tokens accordingly.

Actual support for deferred I/O is missing from the driver. So
writing to memory-mapped pages does not automatically update the
scanout buffer.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jaya Kumar <jayalk@intworks.biz>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231127131655.4020-7-tzimmermann@suse.de