freedreno: don't flush when new and old pfb is identical

freedreno: don't flush when new and old pfb is identical

In the 'inorder' case (ie. FD_MESA_DEBUG=inorder, or old kernel), if the
u_blitter clear path is used (a3xx, a4xx, and some fallback cases on
newer gens), util_blitter_restore_fb_state() will set_framebuffer_state()
to something that is identical to the current fb state, which triggers
an unnecessary flush, and then eventually an assert:

  (gdb) bt
  #0  0x0000007fbf24a078 in kill () from /lib64/libc.so.6
  #1  0x0000007fbe061278 in _debug_assert_fail (expr=0x7fbe93a820 "!batch->flushed", file=0x7fbe93a628 "../src/gallium/drivers/freedreno/freedreno_batch.c", line=491, function=0x7fbe93a990 <__func__.17380> "fd_batch_check_size") at ../src/gallium/auxiliary/util/u_debug.c:322
  #2  0x0000007fbe1ccb8c in fd_batch_check_size (batch=0x55556d5a70) at ../src/gallium/drivers/freedreno/freedreno_batch.c:491
  #3  0x0000007fbe1d0e08 in fd_clear (pctx=0x55555c61e0, buffers=5, color=0x55556e388c, depth=1, stencil=0) at ../src/gallium/drivers/freedreno/freedreno_draw.c:463
  #4  0x0000007fbe57afa4 in st_Clear (ctx=0x55556e17b0, mask=18) at ../src/mesa/state_tracker/st_cb_clear.c:452

The assert was introduced in 4b847b38ae3, so from a functionality
standpoint this patch fixes that commit.  But it should also avoid an
unnecessary flush in the 'inorder' case, fixing a performance bug.

Fixes: 4b847b38ae3 freedreno: make fd_batch a one-shot thing
Signed-off-by: Rob Clark <robdclark@gmail.com>