drm/vc4: Flush the caches before the bin jobs, as well.

If the frame samples from a render target that was just written, its
cache flush during the binning step may have occurred before the
previous frame's RCL was completed.  Flush the texture caches again
before starting each RCL job to make sure that the sampling of the
previous RCL's output is correct.

Fixes flickering in the top left of 3DMMES Taiji.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: ca26d28b

 ("drm/vc4: improve throughput by pipelining binning and rendering jobs")
Link: https://patchwork.freedesktop.org/patch/msgid/20171221221722.23809-1-eric@anholt.net
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>