fbdev/nvidiafb: 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]>
Cc: Antonino Daplas <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/video/fbdev/Kconfig

···
 	tristate "nVidia Framebuffer Support"
 	depends on FB && PCI
 	select FB_BACKLIGHT if FB_NVIDIA_BACKLIGHT
-	select FB_MODE_HELPERS
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select FB_IOMEM_FOPS
 	select BITREVERSE
 	select VGASTATE
 	select VIDEO_NOMODESET

drivers/video/fbdev/nvidia/nvidia.c

···
 	.owner          = THIS_MODULE,
 	.fb_open        = nvidiafb_open,
 	.fb_release     = nvidiafb_release,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
 	.fb_check_var   = nvidiafb_check_var,
 	.fb_set_par     = nvidiafb_set_par,
 	.fb_setcolreg   = nvidiafb_setcolreg,
···
 	.fb_imageblit   = nvidiafb_imageblit,
 	.fb_cursor      = nvidiafb_cursor,
 	.fb_sync        = nvidiafb_sync,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
 };
 
 static int nvidiafb_suspend_late(struct device *dev, pm_message_t mesg)