fbdev/offb: Use fbdev I/O helpers

Set struct fb_ops and with FB_DEFAULT_IOMEM_OPS, fbdev's initializer
for I/O memory. Sets the callbacks to the cfb_ and fb_io_ functions.
Select the correct modules with Kconfig's FB_IOMEM_HELPERS token.

The macro and token set the currently selected values, so there is
no functional change.

v3:
	* use _IOMEM_ in commit message
v2:
	* updated to use _IOMEM_ tokens
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230803184034.6456-29-tzimmermann@suse.de

drivers/video/fbdev/Kconfig

@@ -301,9 +301,7 @@ config FB_OF
 	depends on FB && PPC && (!PPC_PSERIES || PCI)
 	depends on !DRM_OFDRM
 	select APERTURE_HELPERS
-	select FB_CFB_FILLRECT
-	select FB_CFB_COPYAREA
-	select FB_CFB_IMAGEBLIT
+	select FB_IOMEM_HELPERS
 	select FB_MACMODES
 	help
 	  Say Y if you want support with Open Firmware for your graphics

drivers/video/fbdev/offb.c

@@ -293,13 +293,11 @@ static void offb_destroy(struct fb_info *info)
 
 static const struct fb_ops offb_ops = {
 	.owner		= THIS_MODULE,
+	FB_DEFAULT_IOMEM_OPS,
 	.fb_destroy	= offb_destroy,
 	.fb_setcolreg	= offb_setcolreg,
 	.fb_set_par	= offb_set_par,
 	.fb_blank	= offb_blank,
-	.fb_fillrect	= cfb_fillrect,
-	.fb_copyarea	= cfb_copyarea,
-	.fb_imageblit	= cfb_imageblit,
 };
 
 static void __iomem *offb_map_reg(struct device_node *np, int index,