UPSTREAM: drm/rockchip: Unreference framebuffers from flip work

UPSTREAM: drm/rockchip: Unreference framebuffers from flip work

Currently the driver waits for vblank and then unreferences old
framebuffers from atomic commit code path. This is however breaking the
legacy cursor API, which requires the updates to be fully asynchronous.
Instead of just adding a special case for cursor, we can have actually
smaller amount of code to unreference any changed framebuffer from a
flip work.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
(cherry picked from commit 47a7eb4597775ecdc29d2630d875a991f0449bf3)

Change-Id: Id36cdef1ea3962ac8c9a99549732d1810c57c4f9
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>