fbdev/stifb: 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 <tzimmermann@suse.de>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230927074722.6197-39-tzimmermann@suse.de

drivers/video/fbdev/Kconfig

@@ -384,6 +384,7 @@ config FB_STI
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select FB_IOMEM_FOPS
 	select STI_CORE
 	default y
 	help

drivers/video/fbdev/stifb.c

@@ -1167,12 +1167,14 @@ stifb_init_display(struct stifb_info *fb)
 
 static const struct fb_ops stifb_ops = {
 	.owner		= THIS_MODULE,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
 	.fb_check_var	= stifb_check_var,
 	.fb_setcolreg	= stifb_setcolreg,
 	.fb_blank	= stifb_blank,
 	.fb_fillrect	= stifb_fillrect,
 	.fb_copyarea	= stifb_copyarea,
 	.fb_imageblit	= cfb_imageblit,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
 };