radeonsi: simplify and improve flushing

radeonsi: simplify and improve flushing

This mimics r600g. The R600_CONTEXT_xxx flags are added to rctx->b.flags
and si_emit_cache_flush emits the packets. That's it. The shared radeon code
tells us when the streamout cache should be flushed, so we have to check
the flags anyway.

There is a new atom "cache_flush", because caches must be flushed *after*
resource descriptors are changed in memory.

Functional changes:

* Write caches are flushed at the end of CS and read caches are flushed
  at its beginning.

* Sampler view states are removed from si_state, they only held the flush
  flags.

* Everytime a shader is changed, the I cache is flushed. Is this needed?
  Due to a hw bug, this also flushes the K cache.

* The WRITE_DATA packet is changed to use TC, which fixes a rendering issue
  in openarena. I'm not sure how TC interacts with CP DMA, but for now it
  seems to work better than any other solution I tried. (BTW CIK allows us
  to use TC for CP DMA.)

* Flush the K cache instead of the texture cache when updating resource
  descriptors (due to a hw bug, this also flushes the I cache).
  I think the K cache flush is correct here, but I'm not sure if the texture
  cache should be flushed too (probably not considering we use TC
  for WRITE_DATA, but we don't use TC for CP DMA).

* The number of resource contexts is decreased to 16. With all of these cache
  changes, 4 doesn't work, but 8 works, which suggests I'm actually doing
  the right thing here and the pipeline isn't drained during flushes.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Tested-by: Tom Stellard <thomas.stellard@amd.com>