fbdev: Include <linux/io.h> in various drivers

The code uses writel() and similar I/O-memory helpers. Include
the header file to get the declarations.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20230512102444.5438-5-tzimmermann@suse.de