drm/vc4: Don't force new binner overflow allocation per draw.

drm/vc4: Don't force new binner overflow allocation per draw.

This came from the initial bringup code, which always idled the GPU
and always reset the overflow.  That massively increases the size of
the working set when you're doing lots of small draws, though, as is
common on X desktops or piglit.

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