fbdev/atafb: Initialize fb_ops to fbdev I/O-memory helpers

Initialize the instance of struct fb_ops with fbdev initializer
macros for framebuffers in I/O address space. Set the read/write,
draw and mmap callbacks to the correct implementation and avoid
implicit defaults. Also select the necessary I/O helpers in Kconfig.

Fbdev drivers sometimes rely on the callbacks being NULL for a
default implementation to be invoked; hence requiring the I/O
helpers to be built in any case. Setting all callbacks in all
drivers explicitly will allow to make the I/O helpers optional.
This benefits systems that do not use these functions.

No functional changes.

Signed-off-by: Thomas Zimmermann <[e-mail]>
Acked-by: Javier Martinez Canillas <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/video/fbdev/Kconfig

···
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select FB_IOMEM_FOPS
 	help
 	  This is the frame buffer device driver for the builtin graphics
 	  chipset found in Ataris.

drivers/video/fbdev/atafb.c

···
 
 static struct fb_ops atafb_ops = {
 	.owner =	THIS_MODULE,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
 	.fb_check_var	= atafb_check_var,
 	.fb_set_par	= atafb_set_par,
 	.fb_blank =	atafb_blank,
···
 	.fb_copyarea	= atafb_copyarea,
 	.fb_imageblit	= atafb_imageblit,
 	.fb_ioctl =	atafb_ioctl,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
 };
 
 static void check_default_par(int detected_mode)