gallium: add take_ownership param into set_constant_buffer to eliminate atomics

We often do this:
    pipe->set_constant_buffer(pipe, shader, slot, &cb);
    pipe_resource_reference(&cb->buffer, NULL);

That results in atomic increment in set_constant_buffer followed by
atomic decrement after set_constant_buffer. This new interface
eliminates those atomics.

For the case above, this should be used instead:
    pipe->set_constant_buffer(pipe, shader, slot, true, &cb);
    cb->buffer = NULL; // if cb is not a local variable, else do nothing

AMD Zen benefits from this. The perf improvement is ~3% for Viewperf13/Catia.

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8298>

docs/gallium/context.rst

@@ -48,6 +48,8 @@ buffers, surfaces) are bound to the driver.
   type. index is used to indicate which buffer to set (some APIs may allow
   multiple ones to be set, and binding a specific one later, though drivers
   are mostly restricted to the first one right now).
+  If take_ownership is true, the buffer reference is passed to the driver, so
+  that the driver doesn't have to increment the reference count.
 
 * ``set_inlinable_constants`` sets inlinable constants for constant buffer 0.