fbdev/sm712fb: Do not include <linux/screen_info.h>

Sm712fb's dependency on <linux/screen_info.h> is artificial in that
it only uses struct screen_info for its internals. Replace the use of
struct screen_info with a custom data structure and remove the include
of <linux/screen_info.h>.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Cc: Helge Deller <deller@gmx.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230706104852.27451-3-tzimmermann@suse.de