v3d: only process glMemoryBarrier() for SSBOs and images

v3d: only process glMemoryBarrier() for SSBOs and images

PIPE_BARRIER_UPDATE is defined as:
PIPE_BARRIER_UPDATE_BUFFER | PIPE_BARRIER_UPDATE_TEXTURE

Which means we were flushing for any flags other than these two, but
this was intended to only flush for ssbos and images.

Actually, the driver automatically flushes jobs as we need, including
writes/reads involving SSBOs and images, so we don't really need to
flush anything when the program emits a barrier. However, this may
lead to excessive flushing in some cases, so we will soon change this
to avoid atutomatic flushing of the current job for SSBOs and images,
meaning that we will rely on the application to emit correct memory
barriers for these that we should make sure to process here.

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