drm/framebuffer: Acquire internal references on GEM handles

Acquire GEM handles in drm_framebuffer_init() and release them in
the corresponding drm_framebuffer_cleanup(). Ties the handle's
lifetime to the framebuffer. Not all GEM buffer objects have GEM
handles. If not set, no refcounting takes place. This is the case
for some fbdev emulation. This is not a problem as these GEM objects
do not use dma-bufs and drivers will not release them while fbdev
emulation is running. Framebuffer flags keep a bit per color plane
of which the framebuffer holds a GEM handle reference.

As all drivers use drm_framebuffer_init(), they will now all hold
dma-buf references as fixed in commit 5307dce878d4 ("drm/gem: Acquire
references on GEM handles for framebuffers").

In the GEM framebuffer helpers, restore the original ref counting
on buffer objects. As the helpers for handle refcounting are now
no longer called from outside the DRM core, unexport the symbols.

v3:
- don't mix internal flags with mode flags (Christian)
v2:
- track framebuffer handle refs by flag
- drop gma500 cleanup (Christian)

Signed-off-by: Thomas Zimmermann <[email protected]>
Fixes: 5307dce878d4 ("drm/gem: Acquire references on GEM handles for framebuffers")
Reported-by: Bert Karwatzki <[email protected]>
Closes: https://lore.kernel.org/dri-devel/[email protected]/
Tested-by: Bert Karwatzki <[email protected]>
Tested-by: Mario Limonciello <[email protected]>
Tested-by: Borislav Petkov (AMD) <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Anusha Srivatsa <[email protected]>
Cc: Christian König <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Sumit Semwal <[email protected]>
Cc: "Christian König" <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: <[email protected]>
Reviewed-by: Christian König <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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