radv: Do not change scratch settings while shaders are active.

radv: Do not change scratch settings while shaders are active.

When the scratch ringbuffer settings are changed, the shader unit has
to be idle or we will have shaders using old and new settings.

That combination is not supported on the HW (likely the offset is
ringbuffer idx * WAVESIZE * 1024).

CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>