radv: only sync CP DMA for transfer operations or bottom pipe

radv: only sync CP DMA for transfer operations or bottom pipe

CP DMA can only be busy when the driver copies buffers. The
only affected Vulkan commands are vkCmdCopyBuffer() and
vkCmdUpdateBuffer() (because we fallback to a copy depending on
a threshold). Clear operations are currently not concerned
because the driver always syncs after the last DMA operation.

Per the spec, these two operations have to be externally
synchronized with VK_PIPELINE_STAGE_TRANSFER_BIT.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>