fbdev/imsttfb: 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/20230927074722.6197-21-tzimmermann@suse.de

drivers/video/fbdev/Kconfig

@@ -356,6 +356,7 @@ config FB_IMSTT
 	bool "IMS Twin Turbo display support"
 	depends on (FB = y) && PCI
 	select FB_CFB_IMAGEBLIT
+	select FB_IOMEM_FOPS
 	select FB_MACMODES if PPC_PMAC
 	select VIDEO_NOMODESET
 	help

drivers/video/fbdev/imsttfb.c

@@ -1336,6 +1336,7 @@ static struct pci_driver imsttfb_pci_driver = {
 
 static const struct fb_ops imsttfb_ops = {
 	.owner 		= THIS_MODULE,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
 	.fb_check_var	= imsttfb_check_var,
 	.fb_set_par 	= imsttfb_set_par,
 	.fb_setcolreg 	= imsttfb_setcolreg,
@@ -1345,6 +1346,7 @@ static const struct fb_ops imsttfb_ops = {
 	.fb_copyarea	= imsttfb_copyarea,
 	.fb_imageblit	= cfb_imageblit,
 	.fb_ioctl 	= imsttfb_ioctl,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
 };
 
 static int init_imstt(struct fb_info *info)