drm/fbdev-dma: Only install deferred I/O if necessary

drm/fbdev-dma: Only install deferred I/O if necessary

Deferred I/O requires struct page for framebuffer memory, which is
not guaranteed for all DMA ranges. We thus only install deferred I/O
if we have a framebuffer that requires it.

A reported bug affected the ipu-v3 and pl111 drivers, which have video
memory in either Normal or HighMem zones

[    0.000000] Zone ranges:
[    0.000000]   Normal   [mem 0x0000000010000000-0x000000003fffffff]
[    0.000000]   HighMem  [mem 0x0000000040000000-0x000000004fffffff]

where deferred I/O only works correctly with HighMem. See the Closes
tags for bug reports.

v2:
- test if screen_buffer supports deferred I/O (Sima)

Signed-off-by: Thomas Zimmermann <[email protected]>
Fixes: 808a40b69468 ("drm/fbdev-dma: Implement damage handling and deferred I/O")
Reported-by: Alexander Stein <[email protected]>
Closes: https://lore.kernel.org/all/23636953.6Emhk5qWAg@steina-w/
Reported-by: Linus Walleij <[email protected]>
Closes: https://lore.kernel.org/dri-devel/CACRpkdb+hb9AGavbWpY-=uQQ0apY9en_tWJioPKf_fAbXMP4Hg@mail.gmail.com/
Tested-by: Alexander Stein <[email protected]>
Tested-by: Linus Walleij <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Javier Martinez Canillas <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Reviewed-by: Simona Vetter <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]