etnaviv: fix resource usage tracking across different pipe_context's

etnaviv: fix resource usage tracking across different pipe_context's

A pipe_resource can be shared by all the pipe_context's hanging off the
same pipe_screen.

Changes from v2 -> v3:
 - add locking with mtx_*() to resource and screen (Marek)
Changes from v3 -> v4:
 - drop rsc->lock, just use screen->lock for the entire serialization (Marek)
 - simplify etna_resource_used() flush condition, which also prevents
   potentially flushing resources twice (Marek)
 - don't remove resouces from screen->used_resources in
   etna_cmd_stream_reset_notify(), they may still be used in other
   contexts and may need flushing there later on (Marek)
Changes from v4 -> v5:
 - Fix coding style issues reported by Guido
Changes from v5 -> v6:
 - Add missing locking in etna_transfer_map(..) (Boris)

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Marek Vasut <marex@denx.de>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Boris Brezillon <boris.brezillon@collabora.com>