drm/exynos: Use fbdev DMA helpers

Use fbdev's DMA helpers for fbdev emulation. The driver previously
used the I/O-memory helpers, while allocating DMA-able system memory.
This could (in theory) result in bus errors from accessing the memory
range.

This bug has been present since the exynos driver was first added.

v2:
	* drop the pointless Fixes tag (Javier)
	* fix typo in commit message
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Inki Dae <inki.dae@samsung.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Alim Akhtar <alim.akhtar@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230707083422.18691-7-tzimmermann@suse.de

drivers/gpu/drm/exynos/Kconfig

@@ -7,7 +7,7 @@ config DRM_EXYNOS
 	select DRM_DISPLAY_HELPER if DRM_EXYNOS_DP
 	select DRM_KMS_HELPER
 	select VIDEOMODE_HELPERS
-	select FB_IO_HELPERS if DRM_FBDEV_EMULATION
+	select FB_DMA_HELPERS if DRM_FBDEV_EMULATION
 	select SND_SOC_HDMI_CODEC if SND_SOC
 	help
 	  Choose this option if you have a Samsung SoC Exynos chipset.

drivers/gpu/drm/exynos/exynos_drm_fbdev.c

@@ -49,9 +49,9 @@ static void exynos_drm_fb_destroy(struct fb_info *info)
 
 static const struct fb_ops exynos_drm_fb_ops = {
 	.owner		= THIS_MODULE,
-	__FB_DEFAULT_IO_OPS_RDWR,
+	__FB_DEFAULT_DMA_OPS_RDWR,
 	DRM_FB_HELPER_DEFAULT_OPS,
-	__FB_DEFAULT_IO_OPS_DRAW,
+	__FB_DEFAULT_DMA_OPS_DRAW,
 	.fb_mmap        = exynos_drm_fb_mmap,
 	.fb_destroy	= exynos_drm_fb_destroy,
 };