fbdev/vga16fb: 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>
Link: https://patchwork.freedesktop.org/patch/msgid/20230927074722.6197-45-tzimmermann@suse.de

drivers/video/fbdev/Kconfig

@@ -369,6 +369,7 @@ config FB_VGA16
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select FB_IOMEM_FOPS
 	select VGASTATE
 	select FONT_8x16 if FRAMEBUFFER_CONSOLE
 	help

drivers/video/fbdev/vga16fb.c

@@ -1291,6 +1291,7 @@ static const struct fb_ops vga16fb_ops = {
 	.owner		= THIS_MODULE,
 	.fb_open        = vga16fb_open,
 	.fb_release     = vga16fb_release,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
 	.fb_destroy	= vga16fb_destroy,
 	.fb_check_var	= vga16fb_check_var,
 	.fb_set_par	= vga16fb_set_par,
@@ -1300,6 +1301,7 @@ static const struct fb_ops vga16fb_ops = {
 	.fb_fillrect	= vga16fb_fillrect,
 	.fb_copyarea	= vga16fb_copyarea,
 	.fb_imageblit	= vga16fb_imageblit,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
 };
 
 static int vga16fb_probe(struct platform_device *dev)